The Dangers and Costs of Harmful Algal Blooms (HABs) and Cyanobacteria in U.S. Freshwater

From the Great Lakes to backyard ponds, harmful algae blooms caused by toxic cyanobacteria are spreading through freshwater in all 50 states. Around 134,000 lakes now test positive for cyanotoxins. These toxins are in the water your family swims in, the water your dog drinks from, and increasingly, the water that comes out of your tap.

This page covers what the danger actually is, what blooms have cost communities in real dollars, and why the same water blooms again the following year. Every figure below is sourced, and the full source list is at the bottom of the page.

What are harmful algal blooms and cyanobacteria?

What most people call toxic algae is actually cyanobacteria, an ancient microorganism that photosynthesizes like microalgae but is built differently. Cyanobacteria have no cell nucleus and none of the other membrane-bound structures that a true alga carries. That makes cyanobacteria a fundamentally different organism from the beneficial algae and phytoplankton that keep water healthy. When excess nutrients wash into a lake, pond or stream, they feed these cyanobacteria. The cyanobacteria explode into thick, dangerous harmful algae blooms that produce cyanotoxins and poison the water. It happens in the Great Lakes and in backyard ponds alike.

EPA's 2022 National Lakes Assessment rated 50 percent of U.S. lakes in poor condition for phosphorus and 47 percent in poor condition for nitrogen, making nutrient pollution the most widespread stressor it measured. That is roughly 134,000 lakes primed for cyanobacteria blooms right now, and the numbers have climbed in every assessment cycle since 2012. It is important to understand that not all algae are bad. Many species of algae and phytoplankton are essential to healthy aquatic ecosystems. The problem is specifically cyanobacteria, and the excess nutrients that feed them.

Source: EPA, National Lakes Assessment 2022 Key Findings

Where do these excess nutrients come from?

Nitrogen and phosphorus enter waterways from many sources: agricultural runoff, lawn care products, stormwater drains, aging sewer systems and industrial discharge. American agriculture applies roughly 12 million tons of nitrogen and 4 million tons of phosphate each year, and crops do not absorb all of it. Rain washes the excess into nearby lakes, ponds and streams, where it breaks down into the dissolved ammonia, nitrite, nitrate and phosphate that cyanobacteria feed on. Here is the useful part: ammonia, nitrite, nitrate and phosphate are exactly what beneficial phytoplankton consumes, which turns a pollution problem into a recoverable resource.

Sources: EPA, Sources and Solutions: Agriculture; USDA Economic Research Service, Fertilizer Use and Price

Why harmful algae blooms are getting worse every year

Warmer temperatures make cyanobacteria grow faster and bloom earlier. In western Lake Erie, research covering 1995 to 2022 found the bloom season expanding by up to a month and potential cyanobacterial growth rates rising by as much as 30 percent, with the effect strongest in warm, shallow water. NOAA detected cyanotoxins in Lake Erie on April 28, 2025, earlier in the year than in any season on record, and the 2022 bloom ran into November. With millions of ponds on farms and in communities across the country, the problem reaches far beyond the headlines.

Source: Gregory J. Dick, University of Michigan Cooperative Institute for Great Lakes Research, Toxic algae blooms are lasting longer in Lake Erie, June 2025

Cyanotoxins: the poisons hiding in the water

Cyanobacteria produce over 80 known cyanotoxins, and they are more dangerous than most people realize. These cyanotoxins attack the liver, brain, kidneys and skin. Some are linked to cancer, and others are under investigation for links to neurological disease. And here is the part that catches people out: you cannot boil them out, filter them with a household pitcher filter, or destroy them with chlorine. If you or someone close to you is ever exposed, knowing that the cause is cyanobacteria, and saying so, can get you the right medical attention faster.

Sources: EPA, Common Cyanotoxins; CDC, Clinical Signs and Symptoms

The scale of the problem: Harmful algal blooms are spreading faster than ever

Thirty years ago harmful algae blooms were rare. Today cyanobacteria have been found in freshwater lakes, ponds and streams in every state. EPA's 2022 National Lakes Assessment told a stark story: microcystins were detected in 50 percent of lakes nationally, up from 21 percent just five years earlier. Those are only the lakes being sampled. The millions of small ponds on farms, in neighborhoods and at parks are not tested at all.
EPA's assessment represents 268,020 lakes across the country, counting every water body of at least one hectare and one meter deep.

HAB hotspots in every U.S. region

Harmful algae blooms are not limited to a few problem areas. Every region of the United States is affected.

Great Lakes and Midwest (OH, MI, MN, WI, IN, IL). Lake Erie has had annual toxic cyanobacteria blooms since 2002. The 2024 bloom began June 24, the earliest ever recorded, and cyanotoxins were detected as early as April 28, 2025. Inland lakes across Minnesota, Wisconsin, Indiana and Illinois are seeing rapidly increasing HAB events fueled by excess phosphorus and nitrogen.

Southeast (FL, GA, AL, SC, NC). Florida's Lake Okeechobee has been besieged by cyanobacteria for decades, producing blooms that contaminate downstream waterways. The state has committed over $340 million to HAB mitigation. HABs are spreading across freshwater bodies throughout the Southeast as temperatures rise.

Northeast (NY, PA, VT, NH, MA, CT). HABs increasingly affect lakes and reservoirs across New England and the Mid-Atlantic. Lake Champlain, the Finger Lakes and countless smaller ponds and reservoirs are seeing more frequent and more severe cyanobacteria blooms each year.

Pacific Northwest (OR, WA, ID). Salem's 2018 drinking water crisis showed how vulnerable the region is. HABs are increasing across Oregon, Washington and Idaho, and Oregon had no dedicated HAB funding until recently.

West and Mountain States (UT, CO, CA, NV, MT). Utah Lake has carried a warning advisory with microcystin, anatoxin and cylindrospermopsin all detected at once. California's Clear Lake, Colorado reservoirs and mountain lakes across the Rockies are all seeing growing HAB problems driven by warming temperatures and nutrient pollution.

South and Central (TX, OK, KS, MO, AR, LA). Warm climates and agricultural activity make this region highly vulnerable. Texas lakes, Kansas reservoirs and farm ponds across the Great Plains are seeing cyanobacteria blooms start earlier and last longer each year.

Sources: NOAA, Lake Erie HAB Forecasts; EPA, Agriculture Nutrient Pollution; University of Michigan, Lake Erie HABs

How cyanobacteria and cyanotoxins harm people

You can be poisoned by drinking the water, by swimming in it, or by breathing near it. Cyanotoxins from harmful algae blooms in freshwater lakes and ponds affect the liver, brain, lungs and skin. Swallowing the water carries the highest risk, but you do not have to touch the water to be exposed at all. Being near a contaminated pond on a windy day is enough.

Liver damage from microcystin

The most common cyanotoxin, microcystin, attacks the liver, and long-term exposure is linked to liver cancer. Microcystin is now found in half the lakes EPA samples nationally, around 134,000 freshwater lakes.

Brain and nerve damage from cyanotoxins

Breathing problems from aerosolized cyanotoxins

Cyanotoxins can become aerosolized, meaning they turn into tiny airborne particles. Wind carries them off the water surface and into the air, and you can breathe them in just by walking near a contaminated lake or pond. People living near freshwater bodies with harmful algae blooms report coughing, sore throats and asthma-like symptoms without ever going in the water.

Skin and eye irritation from cyanobacteria contact

Touching water contaminated with cyanobacteria causes rashes, hives and painful skin irritation. Eye irritation and stomach illness are common after swimming in freshwater lakes and ponds with active harmful algae blooms.

Sources: CDC, Harmful Algal Blooms and Your Health; NIEHS, Algal Blooms; Oregon Health Authority, Cyanobacteria Blooms FAQ

Drinking water contamination: when a bloom shuts off a city's supply

Toledo, Ohio, August 2014

At 2 a.m. on August 2, 2014, a harmful algae bloom in Lake Erie pushed microcystin through Toledo's treatment plant and the city issued a do-not-drink advisory. As many as 400,000 people could not drink their tap water, cook with it, or boil it. The governor declared a state of emergency. The advisory was lifted on the evening of August 4, roughly two and a half days later. Toledo has since invested $401.7 million in stormwater, wastewater and drinking water treatment infrastructure. Many residents still hesitate over their tap water a decade later.

Salem, Oregon, May 2018

Cyanotoxins from a harmful algae bloom in Detroit Lake passed through Salem's filtration plant and into tap water, triggering a month-long contamination event in the state capital. Bottled water sold out within hours. The governor declared a state of emergency and the National Guard distributed water to residents.

Why boiling water makes cyanotoxin worse

During the Toledo emergency, residents were told specifically not to boil the water. Boiling does not destroy cyanotoxins, and it ruptures the cyanobacteria cells themselves, releasing the toxin that was held inside them. Oregon Health Authority puts it plainly: boiling splits the cells open, they release their toxins, and that makes the problem worse. The same principle explains why killing a bloom does not end it. Whether the cells are ruptured by heat or by copper, what was inside them ends up in the water.

Sources: Statehouse News Bureau; Oregon Public Broadcasting; Oregon Health Authority

Why harmful algal blooms are deadly for dogs, often within hours

Dogs are the most frequent victims of cyanobacteria, because they drink from and play in freshwater ponds, lakes and puddles. It does not matter whether it is a Great Lake or a farm pond; cyanotoxins are just as deadly in a small community pond as in a large reservoir. The hardest part is that a dog can absorb a lethal dose without showing any warning sign until it is too late. There is no antidote for cyanotoxin poisoning.

How pets are exposed to cyanotoxins

Dogs are poisoned by drinking contaminated water, by swallowing bloom material while swimming, or by licking toxic residue off their fur after getting out. Symptoms can appear in as little as one to three and a half hours and progress rapidly to seizures, collapse and death. Watch for vomiting, diarrhea, staggering, lethargy, seizures and sudden collapse. By the time symptoms appear it is often too late for treatment.

Documented dog deaths from harmful algal blooms

Lake Travis, Texas, 2021: two dogs died and five were sickened by cyanotoxin exposure at a popular swimming area.

Michigan, 2019: four dogs died after exposure to cyanobacteria in a private pond.

Kansas, 2011: five confirmed dog deaths from HAB-associated cyanotoxin poisoning.

A national tracking map has recorded at least 32 animal deaths since 2010, and researchers say the true number is far higher because most cases are never reported.

Sources: Cornell Veterinary Medicine; EWG, Dog Deaths Linked to HABs; PMC, Canine Dihydroanatoxin-a Mortality

Wildlife kills and ecosystem collapse due to harmful algal blooms

Harmful algae blooms do not only harm people and pets. They devastate whole aquatic ecosystems. In everything from Great Lakes to backyard ponds, dense cyanobacteria blooms block sunlight, deplete oxygen and create dead zones where fish and other aquatic life suffocate.

Massive fish kills

Maryland documented 391,516 fish deaths in 2022 alone. Fish kills in small ponds, community lakes and farm stock tanks happen constantly without ever being counted. A single harmful algae bloom event can kill every fish in a small pond overnight.

Bird and mammal deaths

Cyanotoxins move through the food chain in ponds and lakes of all sizes. Birds, mammals and livestock that drink from contaminated water are at risk, and small, unmonitored water bodies are the most dangerous, because nobody is testing them.

Eutrophication, hypoxia and dead zones: how a bloom suffocates a pond

Eutrophication is the enrichment of a water body with nitrogen and phosphorus. It is the condition that makes a harmful algae bloom possible, not the damage the bloom does. The damage comes next. A dense bloom shades out everything below it, and at night the bloom itself respires and draws down dissolved oxygen. When the bloom collapses, bacteria decompose the dead cells and consume what oxygen is left. Dissolved oxygen falls to hypoxic levels, then to anoxic ones, and the area becomes a dead zone where fish, insects and other aquatic life suffocate.

In a deep lake this plays out over weeks. In a shallow pond it can happen between sunset and sunrise, which is why pond owners so often find a complete fish kill in the morning after seeing nothing wrong the day before. Ending a bloom by force does not avoid this. A bloom that is killed decomposes exactly the way a bloom that dies on its own does, and it releases its stored cyanotoxins while it goes. Drawing the nutrients down before the bloom forms is what keeps the oxygen in the water.

Sources: WHOI, Fish Kills; Maryland DEQ, 2022 Fish Kill Summary

Airborne exposure of toxic algal blooms: You do not have to touch the water to be exposed

Cyanotoxins can become aerosolized, turning into microscopic airborne particles that travel on the wind. Wind, waves and boat traffic lift them off the surface of contaminated freshwater lakes and ponds and carry them through the air. Researchers have detected cyanotoxins on air filters worn by people simply walking near affected water. Swallowing the water remains the highest-risk exposure, but inhalation is a real route, and it reaches people who never go near the shoreline.

Families living near contaminated freshwater lakes, ponds and reservoirs breathe these aerosolized cyanotoxins without realizing it. Reported symptoms include sore throats, coughing, asthma-like reactions and chronic respiratory irritation, all from living near water with harmful algae blooms rather than swimming in it. State health agencies now advise avoiding activities that aerosolize bloom water, naming water skiing and power boating specifically.

Sources: PMC, Aerosolized Cyanobacteria in the Human Respiratory Tract; Environmental Science and Technology, Toxic Cyanobacteria; Oregon Health Authority

Small ponds and harmful algae blooms: your pond is at risk too

The headlines focus on Lake Erie and Lake Okeechobee, but toxic cyanobacteria are quietly choking thousands of community ponds, farm ponds, small lakes and local swimming spots across the country. There are over 3.5 million ponds on farms and in communities in the United States, and the vast majority are never tested. These smaller waters are often hit hardest, because they get no monitoring, no funding and no attention.

Community and HOA ponds

Stormwater retention ponds and decorative community lakes are prime targets, because they collect phosphorus and nitrogen from lawns, parking lots and storm drains. When blooms appear, children and pets are at immediate risk, and HOAs face stormwater compliance fines of up to $70,000 per month. Many communities resort to expensive, short-lived chemical treatments that only bring the problem back stronger.

Farm ponds and irrigation water

Local fishing spots and swimming holes

With over 2.5 million farm ponds nationwide, agricultural ponds are ground zero for harmful algae blooms. They collect excess phosphorus and nitrogen from fields, nutrients that feed cyanobacteria instead of crops, and blooms clog irrigation equipment and poison livestock water. Beneficial phytoplankton consumes those same nutrients, and during irrigation it can be recovered and returned to the soil as a natural biostimulant.

Small lakes, creeks and swimming areas that families have used for generations are being shut down by harmful algae blooms. Fish kills in small ponds often go unreported, but they destroy local recreation and can indicate dangerous cyanotoxin levels. A single bloom can kill every fish in a small pond and leave it unsafe for months.

Golf course ponds

Nearly 16,000 U.S. golf courses rely on ponds for irrigation and for appearance. Cyanobacteria-choked ponds damage turf quality, clog spray heads, create odors that drive members away, and create liability when golfers or their dogs come into contact with the water. Courses spend thousands annually on chemical treatments that give only temporary relief.

Fish kills, the visible warning sign

When fish start dying it is often the first visible sign that a water body is in serious trouble. Harmful algae blooms deplete dissolved oxygen as they decompose, suffocating fish within hours. Maryland alone documented 391,516 fish deaths in 2022. In small, unmonitored ponds, the ones in your neighborhood, on your farm or at your local park, fish kills happen constantly without ever being counted. A single bloom in a two-acre pond can kill everything in it overnight and turn a community asset into a health hazard.

Beach closures and posted advisories at parks and swimming areas

State parks, county recreation areas and scenic swimming spots are being closed or posted with health warnings at record rates. In 2024, more than 453 beaches were potentially unsafe on at least 25 percent of the days they were tested. Countless small lakes and ponds at campgrounds, RV parks, neighborhood swim areas and rural recreation spots are never tested at all, which leaves visitors unaware they are being exposed.

Sources: Maryland DEQ, 2022 Fish Kill Summary; WHOI, Fish Kills from Freshwater HABs; Environment America, 2024 Beach Report

Cyanobateria, toxic algal bloom in a small pond

Economic Impact: What harmful algal blooms cost communities, utilities and property owners

Harmful algae blooms are not only a health crisis. They are an economic one. Homeowners watch property values fall. Cities spend hundreds of millions upgrading treatment to handle cyanotoxins. Tourism businesses lose entire seasons. And it gets more expensive every year.
Since 2010, U.S. communities have spent more than $1.1 billion on harmful algae bloom treatment, prevention and remediation, documented across 85 locations in 22 states.

Property values crushed by harmful algal blooms

Ohio State University research found that for every one microgram per liter increase in bloom concentration, nearby property values drop 1.7 percent, about $2,205 per home. Homes directly on affected lakes lose 11 to 30 percent of their value. At Buckeye Lake and Grand Lake St. Marys alone, homeowners lost a combined $152 million.

Water treatment costs are rising

Twelve major U.S. cities have spent $289 million upgrading water treatment to handle cyanotoxins. Clear Lake, California saw treatment costs jump 34 percent during bloom season, with residents paying double the affordability threshold for water. Ohio communities alone account for $815 million, 70 percent of all documented HAB remediation spending nationwide.

Tourism and recreation losses

More than 453 beaches were potentially unsafe for swimming on at least 25 percent of tested days in 2024. Ohio alone recorded 1,027 beach closure or advisory days in a single year. When Lake Erie blooms are present, up to 29 percent of fishing trips are canceled, costing Michigan $5.9 million a year in lost angling revenue. Nationally, NOAA estimates that harmful algal blooms cost the U.S. economy at least $82 million a year in closed beaches, closed shellfish beds and reduced fishing, and puts the 2011 Lake Erie bloom alone at nearly $71 million in lost economic benefit.

Sources: EWG, The High Cost of Algae Blooms; ResearchGate, Bloom and Bust; Grist; Environment America, 2024 Beach Report; NOAA, The Untold Story of HABs

Why spending has not solved it: Billions spent, and harmful algal blooms are still spreading

The federal government has spent hundreds of millions studying harmful algae blooms and cyanobacteria. States have spent hundreds of millions more managing them. The problem is still growing, because most of that investment has gone into monitoring and understanding blooms rather than removing the nutrients that cause them.

Federal HAB research spending

A 2017 GAO audit found that 12 federal agencies spent $101 to $110 million on HAB activities in just fiscal years 2013 through 2015. NOAA alone spent an estimated $168 million between 2013 and 2021. EPA, NSF, USGS and NIH spend millions more annually on cyanobacteria and cyanotoxin research.

Sources: GAO-17-119; Congressional Research Service Report R46921

State HAB remediation spending

Ohio's H2Ohio program spent $135 million annually, recently cut by 40 percent. Florida has committed over $340 million in HAB mitigation grants. Blooms in Lake Erie and Lake Okeechobee continue regardless. Ohio would need an additional $170 to $250 million per year just to meet its phosphorus reduction targets.

Sources: E&E News; WUSF

Why chemical algaecides make the problem worse

Chemical algaecides kill cyanobacteria on contact, but they do not remove the phosphorus and nitrogen that caused the bloom. The nutrients stay in the water and the bloom returns, often stronger. Worse, when the cells are killed they burst open and release their stored cyanotoxins into the water, which makes it more dangerous rather than less.

The damage goes deeper than that. Algaecides also kill the beneficial algae and phytoplankton that are the primary producers of the lake, along with the zooplankton that graze on them. That dismantles the food chain from the bottom up and removes the very organisms that naturally compete with cyanobacteria and hold it in check. Copper-based products then accumulate in the sediment, contaminating the water body long term.

Source: ScienceDirect, Release of algae organic matter following algaecide application

Who is affected by harmful algal blooms?

If you are connected to freshwater in any way, harmful algae blooms and cyanobacteria affect you. Here is who is paying the price right now.

Lakeside homeowners

You bought your home for the water. Harmful algae blooms are dropping property values 11 to 30 percent and making it unsafe to swim, fish, or let your children play near the shore.

Cities and water utilities

Blooms pose serious liability to municipalities and water utilities. When cyanotoxins contaminate a public supply the consequences are enormous: emergency declarations, lawsuits, infrastructure overhauls costing hundreds of millions, and long-term damage to community health and trust. That exposure grows every year as blooms become more frequent.

Parks and recreation

Over 453 beaches were unsafe on 25 percent or more of the days tested in 2024. Ohio alone had 1,027 closure days in a single year. Families are losing their swimming spots to cyanobacteria.

Farmers and ranchers

Excess phosphorus and nitrogen wash off fields into ponds and streams, where they feed cyanobacteria instead of crops. That is lost nutrient and lost money. Beneficial phytoplankton consumes those same nutrients and turns them into more phytoplankton, and during irrigation that phytoplankton-rich water becomes a natural biostimulant that returns the captured nutrients to your soil.

Golf courses

Nearly 16,000 U.S. golf courses deal with harmful algae blooms in their ponds. Cyanobacteria clogs irrigation equipment, degrades turf quality, drives members away with odor, and creates liability when a member's dog drinks from a contaminated pond.

HOAs and communities

That green, smelly pond in the neighborhood is not just unsightly, it is potentially toxic cyanobacteria. HOAs face fines of up to $70,000 a month for stormwater violations, and blooms drag down property values across the whole community.

Solutions for harmful algae blooms: there is another option, and it is biological

Conventional approaches treat the symptom or the watershed. Dredging, alum treatment and watershed nutrient control all work, and all of them are slow, expensive or temporary. Hydralife offers another option, a biological one that draws the nutrients out of the water column itself.

Hydralife's multi-species beneficial phytoplankton consumes the same ammonia, nitrite, nitrate and phosphate that cyanobacteria feed on, 24-7 through the growing season, so the bloom is starved of its food source rather than poisoned.

This approach is called competitive exclusion. Nothing is applied to kill the cyanobacteria. The phytoplankton simply consumes the ammonia, nitrite, nitrate and phosphate first, and the bloom is left without the food supply it needs to form.

It works in freshwater lakes, ponds and reservoirs of any size. For farms, ranches and golf courses, it captures lost nutrients from runoff and returns them to the soil as a natural biostimulant during irrigation. Nutrient-rich water is not a hard case for this approach. It is the condition it is built for.

Find out what is in your water

Every pond, lake and reservoir carries a different nutrient load, and the only way to know yours is to measure it. Tell us about your water body, including its history, size and water source, and send a photo if you have one, and we will recommend a dose and protocol matched to it. Free nutrient testing is available on samples you ship back to us, before and after treatment, so you can verify the drawdown in your own water.

Request a Free Water Analysis

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Call (303)219-0623 or email service@hydralifesolutions.com