Water is critical to the diverse habitats and working landscapes of the Lake Champlain Basin. The region’s climate provides enough rainfall to feed 14,700 miles of streams and rivers and fill Lake Champlain with 6.8 trillion gallons of water. Vibrant communities, outstanding recreational opportunities, and a strong environmental ethic that rely on this abundance of water attract more people to the Lake Champlain Basin each year. Pressures from human activities, however, threaten to degrade water quality.


Pathogens continue to impair water quality and are costly to eliminate, but recent efforts have helped to identify and eliminate some threats.

It is usually best for cities and towns to maintain separate pipe networks for stormwater and sanitary sewage. In cases where there is just one pipe network—a combined sewer system —both flows are combined as they are conveyed to a wastewater treatment facility. When heavy rainfall generates more stormwater runoff than can be accommodated by these combined systems, treatment facilities can be overwhelmed by the high volume of water; untreated or partially treated sewage may then enter the tributary network and eventually the Lake through overflow pipes. These events, known as combined sewer overflows (CSOs), are sources of coliform bacteria and nutrients to the Lake.

Substantial efforts have been made to reduce the number of CSO events in the Basin. Since 1990, the number of CSO discharge points, or outfalls, in Vermont has decreased from 178 to 53. That number is expected to drop even further as a result of a CSO Rule adopted by Vermont Department of Environmental Conservation in 2016. CSOs in the New York portion of the Basin also have declined, with the City of Plattsburgh alone eliminating fifteen CSO outfalls since the 1970s. Long Term Control Plans are in place to address the remaining eleven discharge points in Plattsburgh to mitigate their impact.

Additional efforts are underway to better understand and address the sources of coliform bacteria in the Basin’s waterways, including waste from farm animals, wildlife, pets, and humans. The City of Plattsburgh, for example, used DNA tracking technology to determine the source of coliform bacteria that led to public beach closures along the city’s Lake Champlain shoreline. The study found that gulls and cows were the most common sources of coliform bacteria during dry weather conditions and after rainstorms that did not result in CSOs. After storms that caused CSOs, the most common sources were gulls, humans, and dogs.

Combined sewer overflow

Combined sewer overflows remain a particularly difficult water quality challenge because of the high cost of separating storm and sanitary sewers. Photo: City of Plattsburgh.

Cyanobacteria blooms are not present most days in the Lake Champlain Basin, but warm weather blooms continue to present a challenge.

causes of cyanobacteria infographicCyanobacteria 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 a nuisance when growth is accelerated by calm, warm weather and excessive levels of nutrients such as nitrogen and phosphorus. A cyanobacteria bloom occurs when colonies of cyanobacteria become large enough to see with the naked eye. These colonies typically look like small green pinhead-sized balls and can form a layer (or bloom) on the surface of the water that sometimes resembles thick pea soup.

Severe cyanobacteria blooms sometimes produce toxins that are harmful to humans, pets, and wildlife and can have adverse effects on the Lake Champlain ecosystem, such as reduced oxygen levels in the water and noxious odors. A recent LCBP-supported study that collected fish during blooms did not detect cyanotoxins in Lake Champlain fish tissue, though scientists are still investigating potential impacts to the Lake’s fishery. In addition, tests of drinking water in Vermont public treatment facilities found no detectable presence of cyanotoxins in raw or treated drinking water in summer of 2017.

Toxins produced by cyanobacteria blooms can make the Lake’s water near blooms unsafe for swimming. The LCBP works in partnership with the Lake Champlain Committee, Vermont Department of Environmental Conservation, and Vermont Department of Health (DOH) to support the Lake Champlain Volunteer Cyanobacteria Monitoring Program. During the warm months, more than a hundred 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 Cyanobacteria Tracking Map hosted by Vermont DOH. If the bloom is at a public beach, water samples are tested to determine whether the beach is safe for swimming. Local authorities are notified if test results merit closure of the beach.

cyanobacteria bloom on beach

Cyanobacteria blooms can limit the use of beaches on Lake Champlain. Photo: LCBP.

Figure 3

Figure 3 | Cyanobacteria alerts, 2015-2017

Cyanobacteria blooms are not present most days in Lake Champlain (Figure 3). Blooms occur most frequently from July to August and in shallower, warmer bays of the Lake, such as Missisquoi and St. Albans Bays. When exceptions occur, it is generally due to unusual circumstances. In the fall of 2017, unseasonably warm temperatures, low wind speeds, and excessive nutrients resulted in localized cyanobacteria blooms in many parts of the Lake and in other smaller lakes in the Basin. A bloom in Lake Carmi, Vermont, was especially persistent and intense during this time and continued late into the fall. In addition, Scytonema, a type of cyanobacteria that is rarely observed, was identified in a portion of Burlington Bay for the first time and persisted for several weeks in September and October 2017.

Limiting the levels of nutrients such as phosphorus is critical in combating cyanobacteria blooms in Lake Champlain, and the LCBP and its partners are working to address this root cause.