United States Harmful Algae Bloom Tracker 2026

Why this toxic algae map exists

Every dot on this map represents a harmful algae bloom (HAB) event, warning, or caution issued in 2026 by a state agency, federal body, county health department, or credible news source. These are not predictions. They are publicly issued advisories.

Harmful algae blooms, also called HABs or toxic algae blooms, are caused by the explosive growth of certain cyanobacteria species (also known as blue-green algae) in freshwater lakes, ponds, reservoirs, and slow-moving rivers. They feed on excess nutrients in the water (nitrogen and phosphorus from agriculture, lawns, septic systems, and wastewater) and can release a range of potent toxins that sicken or kill humans, pets, livestock, and fish.

The toxins these blooms release

• Microcystins (produced by Microcystis, Anabaena, Planktothrix): the most common cyanotoxin in U.S. freshwater. A liver toxin and possible human carcinogen; also damages kidneys and the gut. Causes nausea, vomiting, abdominal pain, fever, headache, and skin rashes.

• Cylindrospermopsin (Cylindrospermopsis, Aphanizomenon): attacks the liver and kidneys, causes serious DNA damage, and disrupts developmental processes.

• Anatoxin-a / anatoxin-a(s) (Anabaena, Aphanizomenon): fast-acting neurotoxins. Historically nicknamed "Very Fast Death Factor": animals can die within minutes of exposure. Implicated in many dog deaths at U.S. lakes.

• Saxitoxins: potent neurotoxins. Symptoms range from tingling and numbness to respiratory failure and death.

• BMAA (beta-methylamino-L-alanine): produced by many cyanobacteria. Chronic, repeated exposure is linked to neurodegenerative disease, including ALS, Parkinson's, and Alzheimer's-type illness.

Severity develops over time

Toxin levels are not constant. Many HAB toxins are stored inside algae cells and are released into the water only when those cells die or rupture, which happens naturally as the bloom ages, and can be accelerated by wave action, sudden weather shifts, or chemical algaecide treatment. An aging or treated bloom often releases far more toxin than the active bloom did at its peak. What looks like a mild bloom on Monday can be at its most dangerous a week later.

HAB toxins can travel through the air

They do not stay in the water. Bursting bubbles at the surface, wave action, jet skis, and boats all launch toxin-carrying aerosols into the air. Microcystin and BMAA aerosols have been detected in the air near freshwater blooms and can trigger coughing, wheezing, chest tightness, eye irritation, and asthma flares. People who live, work, or recreate near an affected lake or reservoir, not just swimmers, boaters, and their pets, can be exposed.

This page is updated as new advisories are issued. The earliest freshwater bloom of 2026 on Cayuga Lake (NY) was confirmed April 23, months ahead of the historical norm.

How Hydralife is different from algaecides

Conventional algaecides (copper sulfate, peroxide-based products, and similar) kill algae cells, which sounds good but actually releases the intracellular toxins all at once into the water, causing toxin spikes that can be more dangerous than the original bloom. Hydralife Solutions takes a different approach: we introduce natural, chemical-free competitors that out-consume the nutrients (nitrogen and phosphorus) the harmful algae feed on, starving the bloom rather than killing it chemically. The result is cleaner water with no toxin spike, no harm to fish or beneficial organisms, and longer-lasting improvement.

Learn more about our approach at hydralife.org, or watch how it works on our YouTube channel.

What to do if you, your pet, or your livestock are exposed

If you suspect HAB exposure, the most important step is to stop contact, rinse off, and watch closely for symptoms. The information below is general guidance. Always defer to your physician, your veterinarian, your local poison control center, and your state or county health authority for medical decisions.

What does HAB exposure feel like in humans?

Symptoms depend on the toxin and the route of exposure. Skin contact can cause rashes, hives, blisters, and eye irritation. Swallowing contaminated water can cause stomach pain, nausea, vomiting, diarrhea, headache, and fever. Breathing aerosolized toxins (from surf, jet skis, or waves) can cause coughing, wheezing, chest tightness, shortness of breath, and asthma flare-ups, especially for people with existing lung conditions. People with liver or kidney disease are at higher risk for serious effects from microcystins. If symptoms are severe or worsening, seek medical care immediately.

I think I was exposed. What do I do right now?

Leave the water and the immediate area. Move upwind if you can smell or feel an aerosol. Rinse off thoroughly with clean fresh water and soap, and wash swimsuits and gear separately. Do not eat fish caught from a bloom-affected water body, and do not drink the water. Watch for symptoms over the next 24 hours. If symptoms appear, call your physician or, in the United States, Poison Control at 1-800-222-1222. For severe symptoms (breathing difficulty, persistent vomiting, neurological symptoms), call 911.

My dog drank from a lake or swam in suspected algae. What now?

HABs are especially dangerous to dogs. Anatoxin-a can kill a dog within minutes; microcystin can cause acute liver failure within hours. Act immediately: rinse your dog thoroughly with clean fresh water (wear gloves so you do not contaminate yourself), do not let them lick their fur, and call your veterinarian or an emergency vet right now. Do not wait for symptoms. Symptoms to watch for: weakness, staggering, vomiting, diarrhea, drooling, seizures, difficulty breathing, blue gums, collapse. The ASPCA Animal Poison Control Center is reachable 24/7 at 1-888-426-4435 (a consultation fee may apply).

What about cattle, horses, or other livestock that drink from a pond?

Livestock deaths from HAB-affected stock ponds are a recurring cause of agricultural loss across the United States. If you suspect a bloom, fence off the water immediately and provide an alternate clean source. Move animals out of the affected pasture. Call your veterinarian and your state agricultural extension office to test water and tissue. Symptoms include weakness, staggering, muscle tremors, photosensitization (skin damage on light-colored areas), bloody diarrhea, and sudden death. Document everything (timestamps, symptoms, water appearance, photos). Agricultural insurance and state agencies will ask.

What does a HAB actually look like?

A HAB can look like spilled paint, pea soup, green or blue-green scum, a thick mat on the surface, or streaks and clumps in the water. Colors range from bright green to blue-green, brown, or even purplish. The water may smell musty, earthy, or like rotting plants. Not all green water is harmful, and not all harmful blooms look obvious. When in doubt, stay out, and report what you saw.

Is it safe to eat fish I caught from a bloom-affected lake?

During a bloom or active advisory, do not eat fish from the affected water body. HAB toxins can accumulate in fish tissue, especially in the liver and other organs, and cooking does not destroy them. After an advisory is lifted, follow your state agency's specific guidance. Many recommend cleaning fish carefully, discarding skin, fat, and organs, and eating only the fillet.

How do I report a suspected bloom?

Most U.S. states have an online reporting form for suspected HABs, typically through the state environmental agency or health department. The EPA also runs bloomWatch, a citizen reporting app. When you report, include location (GPS or address), date and time, photos, water appearance, any dead fish or wildlife, and contact info for follow-up. Local news outlets and your county health department are also useful escalation channels, especially if you see official advisories missing on a clearly affected water body.

Can my drinking water be affected?

Yes. Public drinking-water utilities that draw from a HAB-affected lake or reservoir can have toxins (especially microcystin) cross the treatment plant if filtration is not designed for cyanotoxins. Utilities are required to monitor and notify the public if a do-not-drink or do-not-boil order is issued (boiling does not destroy cyanotoxins; it can concentrate them). Private well users near a bloom should also be cautious, especially if shallow groundwater connects to the surface water body. Follow your utility's notifications.

Sources: U.S. EPA, Learn About Harmful Algae; EPA, Common Toxins Produced by Cyanobacteria, Dinoflagellates, and Diatoms; NIH PMC, Adverse Health Effects of Microcystins and Other HAB Toxins; NIH PMC, HAB Aerosols and Human Health.

Educational content; not medical advice.