Clean Water


Since 2013, 95% of routine visual assessments on Lake Champlain during the recreational season reported conditions free of cyanobacteria blooms. Cyanobacteria conditions vary significantly among lake segments, and warm weather blooms continue to present a challenge to recreation and public health.

Cyanobacteria are a group of primitive bacteria that are native to nearly every ecosystem on Earth. Several species of cyanobacteria are found in Lake Champlain, and most of the time they do not cause harm. Cyanobacteria can become harmful and impact recreation when their growth is accelerated by calm, warm weather and excessive levels of nutrients such as nitrogen and phosphorus.

Cyanobacteria blooms infographic

A cyanobacteria bloom occurs when colonies of cyanobacteria become large enough to see with the naked eye and form a surface scum. These colonies often look like green pinhead-sized balls and can form a layer on the surface of the water that may resemble thick pea soup or a paint spill. Cyanobacteria blooms can sometimes produce toxins (known as cyanotoxins) that can be harmful if ingested by humans, pets, or wildlife. Cyanobacteria blooms also can have other adverse effects on Lake Champlain, such as reduced oxygen levels in the water and noxious odors.

aerial photo of a cyanobacteria bloom
An aerial photo of a cyanobacteria bloom in progress. Photo: University of Vermont Spatial Analysis Lab

The LCBP works with the Lake Champlain Committee and Vermont and New York state partners to support the Lake Champlain Cyanobacteria Monitoring Program. During the warm months, more than 100 community scientist volunteers report each week on water conditions along the shoreline. If a cyanobacteria bloom is visible, an alert is posted online to the Lake Champlain CyanoTracker Map hosted by the Vermont Department of Health. If the bloom is at a public beach, it is recommended that the beach is closed to swimming as a precautionary measure, even if cyanotoxin concentrations are not known. In many cases, water samples are tested for cyanotoxins to determine whether the beach is safe for swimming, and local authorities are notified if test results merit closure of the beach.

Cyanobacteria blooms are not present most days in Lake Champlain, and over 95% of the approximately 9,500 routine visual assessment reports submitted since 2013 have reported “generally safe” conditions during the recreational season (Figure 4). Bloom frequency and intensity varies drastically among Lake regions; 98% of reports from Main Lake locations since 2013 indicated “generally safe” conditions while that figure is 77% and 79% for St. Albans and Missisquoi Bays, respectively.

Figure: Cyanobacteria monitoring reports on Lake Champlain
Figure 4 | Cyanobacteria monitoring reports on Lake Champlain

Recent cyanobacteria blooms have impacted recreation opportunities for residents and visitors. In the summer and fall of 2020, extended periods of warm and calm conditions caused cyanobacteria blooms and beach closures in many regions of Lake Champlain, including the Burlington area. Unfortunately, climate change may increase these periods of warm and calm conditions to make increasingly favorable conditions for blooms in the future.

Cyanotoxins are rarely detected in Lake Champlain, though it is best to avoid areas with active cyanobacteria blooms.

Laboratory results from Lake Champlain water samples have shown that when there is no cyanobacteria bloom visible, cyanotoxins are very rarely detected and have never been measured above recreational thresholds for public safety. In addition, cyanotoxins are often not detected in water when cyanobacteria blooms are visible. During the 2018–2020 time period, cyanotoxins were detected in 12 of the 262 water samples tested, and all samples were well below public safety recreational threshold levels.

Since 2015, the 22 Lake Champlain-sourced public water supply systems in Vermont each have voluntarily tested raw and finished (treated) water for cyanotoxins during the warm months. Among over 1,300 samples from these facilities in the summers of 2018–2020, there were no detections of cyanotoxins in finished drinking water samples and two low-level detections of cyanotoxins in raw water samples, which were not confirmed upon repeated sampling.

A recent study found no cyanotoxins in Lake Champlain fish tissue.

The RPI Darrin Fresh Water Institute recently collected Lake Champlain fish during low- and high-severity cyanobacteria blooms and analyzed fish tissues for three types of cyanotoxins: microcystin, anatoxin-a, and cylindrospermopsin. None of these cyanotoxins were detected among the 5 species and 153 specimens sampled, suggesting that these cyanotoxins did not accumulate in fish tissue in Lake Champlain.

There is ongoing work to determine the potential impact of cyanobacteria blooms and associated cyanotoxins on water quality and public health.

In addition to the Lake Champlain Cyanobacteria Monitoring Program, partners in the Basin are pushing the envelope to inform our understanding and management of cyanobacteria blooms. The University of Vermont is at the forefront of this research, with projects that will use drones to determine the extent of cyanobacteria blooms and satellite images to study the distribution and severity of cyanobacteria blooms across Lake Champlain. There are also studies that will continue to measure cyanotoxins in fish tissue, determine whether cyanotoxins might aerosolize and impact shoreline air quality, and determine public perception of cyanobacteria blooms in their communities.

The LCBP and its partners are addressing the root cause of cyanobacteria blooms in Lake Champlain by working to limit the levels of nutrients available for their growth.