Tracking and Understanding Cyanobacteria in Lake Champlain
July 2026 Lake Look
Each summer, thousands of people turn to the Cyanobacteria Tracker before heading to the lake. Some days the map is filled with blue "generally safe" reports. Other days, yellow and red alerts remind us that conditions can change quickly. While blooms that turn the water green may seem like a modern problem, the organisms behind them have existed for billions of years. The story of cyanobacteria is much older than Lake Champlain itself and understanding that story helps explain why blooms are becoming more common today.
What are Cyanobacteria Blooms?
Cyanobacteria, often called “blue-green algae,” are among Earth’s oldest life forms. They evolved not just before humans or mammals, but before our oxygen-rich atmosphere even existed. Over three and a half billion years ago, cyanobacteria were the first organisms to perform photosynthesis. By capturing sunlight and releasing oxygen, they transformed Earth’s atmosphere and paved the way for complex life. Without cyanobacteria, our planet would be unrecognizable, lacking oxygen and diverse life forms that now inhabit it.
These ancient organisms still inhabit nearly every freshwater system, including Lake Champlain. Under normal conditions, they exist alongside countless other microscopic organisms. However, humans began to alter the lake and the landscape around it. Excess nutrients entering the water, combined with warmer temperatures, abundant sunlight, and periods of calm weather, create ideal conditions for cyanobacteria to reproduce rapidly and outcompete other organisms.
When this happens, cyanobacteria can accumulate at the water’s surface or along shorelines, forming a bloom. Blooms may appear as cloudy or murky water, surface scums, or thick mats that may be green, blue-green, yellow-green, or even brown.
Some cyanobacteria species have the ability to produce cyanotoxins that can make pets, wildlife, and people sick. Blooms become a concern because they concentrate large numbers of cyanobacteria and, when toxins are present, can expose people and animals to much higher toxin levels through contact with or ingestion of affected water.
The challenge is that toxicity isn’t visible—there’s no way to tell just by looking whether a bloom is harmful or harmless. Because of this uncertainty, it is important to take a precautionary approach and avoid all contact with blooms. Even blooms that aren’t toxic can disrupt the lake’s natural balance by shading out aquatic plants, starving the water of oxygen, and stressing local fish and invertebrates. What was once a rare annoyance has become a persistent signal that the system is under strain.
Why are we seeing blooms now?
Today’s blooms are not due to new species but rather to imbalances in the lake ecosystem. As humans build roads, clear forests, intensify farming, and develop shorelines, we damage natural processes that ordinarily cycle some nutrients away from water. This paves the way for agricultural runoff, eroding streambanks, over-fertilized lawns, urban stormwater, and outdated septic systems to accelerate the flow of nutrients into Lake Champlain. Essentially, we are overfeeding the lake.
At the same time, climate change is creating longer growing seasons, warmer water temperatures, and more frequent periods of intense weather events—all conditions that favor cyanobacteria growth. Together, excess nutrients and a changing climate are making blooms more frequent, more widespread, and, in some years, longer-lasting.
What’s the Tracker?
For over twenty years, the Lake Champlain Committee (LCC) has coordinated one of the region’s most comprehensive cyanobacteria monitoring programs, in collaboration with partners at the Vermont Department of Environmental Conservation and Vermont Department of Health, and with significant funding through the Lake Champlain Basin Program and NEIWPCC.
Each summer, volunteers trained by LCC monitor hundreds of shoreline locations, observing conditions, reporting changes, and helping maintain a consistent picture of bloom activity throughout the lake – in New York and Quebec, as well as Vermont. These observations contribute to the publicly accessible Cyanobacteria Tracker, and the data informs beach closures, guides recreational safety, and supports environmental research. The cyanobacteria monitoring program is a model of community science that is practical, effective, and deeply rooted in stewardship.
Staying Informed
In addition to checking the tracker, you can sign up to receive LCC's free weekly cyanobacteria reports throughout the monitoring season for summaries of lake conditions, bloom trends, and educational resources. You can also visit LCC’s website to learn how to recognize cyanobacteria and what distinguishes it from common look-alikes such as filamentous green algae, duckweed, and pollen.
Cyanobacteria, after all, are not going anywhere. They are a natural part of freshwater ecosystems and have been for billions of years. But the conditions that allow them to bloom and cause harm are just as persistent. Our ability to decide on land use and water management can reshape Lake Champlain’s future to be less green and murky.
Lake Look is a monthly natural history column produced by the Lake Champlain Committee (LCC). Formed in 1963, LCC is a bi-state nonprofit that uses science-based advocacy, education, and collaborative action to protect and restore water quality, safeguard natural habitats, foster stewardship, and ensure recreational access. You can join, renew your membership, make a special donation, or volunteer to further our work.