Hydralife Results: How Denver's Lake Management Program Lifted a Toxic Algae Advisory at Lily Pond

Denver takes its lakes seriously. The city's Lake Management Program looks after more than two dozen lakes across the City and County of Denver, keeping them healthy and safe so residents and visitors can fish, paddle, and enjoy them all summer. Keeping that many urban water bodies in good condition, year after year, is quiet and demanding work. This is the story of one small pond, a posted health advisory, and an experienced lake manager who was open to a new tool.

A children's fishing pond with a toxic algae problem

Lily Pond is a small, aerated pond on the northeast side of Washington Park in Denver, set aside as a fishing spot for children fifteen and under. It sits at the end of the park's treated water supply line, which leaves it prone to high nutrients and a history of cyanobacteria, the organisms behind harmful algal blooms. In mid May 2026 the pond carried a posted public health advisory asking people and pets to stay out of the water because of toxic algae. For a pond meant for kids, that is exactly the problem worth solving.

A program that knows its water

Denver's Lake Manager has led the city's Lake Management Program for nearly three decades, and he selected Lily Pond specifically because it runs hot with cyanobacteria. That kind of judgment, knowing which water body needs attention and when, is what keeps a system of more than two dozen lakes in good standing. He gave Hydralife the opportunity to address the nutrients driving the bloom.

A beautiful children fishing pond that was made safe from habs through beneficial phytoplankton.

How beneficial phytoplankton works against a bloom

Toxic cyanobacteria bloom when a pond carries more nitrogen and phosphorus than the system can hold in check. Hydralife's approach does not use algaecides. Instead, it introduces live concentrated beneficial phytoplankton that competes directly with cyanobacteria for the ammonia and phosphate both need to grow. Starve the bloom of those nutrients and it loses its advantage. Because Lily Pond began with a high nutrient load, it was a strong candidate for the method.

What happened over the season

Hydralife recorded a baseline in mid May, confirmed the pond was high in nutrients, and applied a inoculation of 100 gallons of concentrated phytoplankton during a warm, sunny stretch to give the phytoplankton the fastest possible start against the cyanobacteria. From late May through the growing season the nutrient readings fell steadily. By early June, ammonia and phosphate were close to undetectable, and they held at those low levels through the summer.

At baseline the pond read ammonia 0.5 ppm with phosphate measuring at .25ppm. By July 8 the water chemistry was stable and the nutrients sited above were close to undetectable. The pond was also visibly alive, with three kinds of fish fry and fingerlings and even a baby crawfish spotted along a single small stretch of shoreline.

The advisory lifted

By late June, Denver's Lake Manager confirmed that a visual inspection showed the cyanobacteria was no longer toxic and had, in his words, had been neutralized. Hydralife kept monitoring and testing the water through the season. Lily Pond held its low nutrient levels and did not post another cyanobacteria advisory.

We only have a visual inspection of the cyanobacteria and whether it is toxic. It is not toxic, so it has been at least neutralized.

Lake Manager, Denver Parks and Recreation, June 2026

Credit to the program

This result belongs to the Denver Lake Management Program and to a lake manager willing to bring a new, chemical free method to a sensitive public pond. Returning a children's fishing pond to a safe and vibrant condition, without copper or peroxide, is the kind of stewardship that keeps Denver's lakes worth visiting. Across more than two dozen water bodies, that steady care is easy to overlook and well worth celebrating.

A note on method

Hydralife manages water biologically. Chemical controls work by killing algae, which returns the dead cells and their nutrient load to the water to feed the next bloom. Beneficial phytoplankton works the other way, by outcompeting nuisance and harmful growth for the nutrients it needs to live. It is a different category of solution, engineered for the high nutrient waters where chemical programs tend to struggle.

Managing a lake with a bloom?

If your city, park, or HOA is managing a lake with a harmful algal bloom or a history of cyanobacteria, Hydralife can help you understand whether beneficial phytoplankton is a fit. Learn more at www.hydralife.org or send us a note at service@hydalifesolutions.com