What's Really Behind the Bloom?

In the quiet hours of early morning, Lake Champlain can appear untouched, almost primeval. A breeze dances across the surface, loons call in the distance, and for a moment it’s easy to picture the lake as it might have looked centuries ago, framed by mountains on either side. But by afternoon, especially on hot, calm days, that illusion sometimes fades into green. Murky, mottled water drifts in ribbons or clusters into scummy slicks. These are cyanobacteria blooms, which are becoming more common and increasingly concerning. Yet, despite public health warnings and efforts to reduce the flow of excess nutrients that fuels the blooms, many people don’t realize the contradiction at the center of it all: cyanobacteria are native, not invasive.  They are a part of the lake’s most ancient lineage, predating the oldest fossils embedded in the rocks along the lake’s shore. 

Our First Breath 

Cyanobacteria, often called “blue-green algae,” are among the oldest forms of life on Earth. Their story begins not just before humans or mammals, but before our oxygen-rich atmosphere even existed. Over three and a half billion years ago, cyanobacteria developed the revolutionary ability to perform photosynthesis. By capturing sunlight and releasing oxygen as a byproduct, 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.  

For most of their existence, cyanobacteria have lived quietly, serving as the microscopic foundation of aquatic ecosystems. These ancient organisms still inhabit nearly every freshwater system, including Lake Champlain. They were never meant to dominate these waters, but that changed when humans began to alter the lake and the landscape around it. 

Feeding the Bloom 

Today’s blooms are not due to completely new species but rather to shifting balances in the lake ecosystem. Warm, calm waters combined with excess nutrients–particularly phosphorus–create ideal conditions for these microscopic organisms to reproduce rapidly. The result is a visible bloom that can discolor the water, deplete oxygen levels, release toxins, and disrupt both recreation and ecology.  

The nutrients that fuel cyanobacteria blooms come largely from land. 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. In simple terms, we are overfeeding the lake, and cyanobacteria are responding. 

Some blooms produce cyanotoxins that can make pets, wildlife, and people sick. 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. 

Still, cyanobacteria are not the enemy. In the right context, they play an important role in cycling nutrients and supporting microbial communities. The problem is not the presence of cyanobacteria but the conditions that allow them to dominate.  

Get Involved 

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 from 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. These observations contribute to the publicly accessible Vermont 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. 

Anyone interested in protecting the lake can participate in the monitoring program. Volunteers receive training and support, committing to weekly observations during the season. The work is straightforward but vital: it connects residents to the health of the lake and creates a detailed record that helps scientists and policymakers better understand and respond to changing conditions. 

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. Let’s stop feeding the problem and start feeding solutions.