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Missisquoi Bay Background

Missisquoi Bay (Vermont and Québec) is an international watershed within the Lake Champlain Basin. It has one of the highest in-lake phosphorus concentrations of any segment of Lake Champlain. Phosphorus loads to and ambient levels in the bay greatly exceed the target levels called for in water quality criteria for phosphorus endorsed by the governments of Vermont, Québec, and New York. Further, this phosphorus contributes significantly to blue-green algae blooms (cyanobacteria) in Missisquoi Bay during the summer months. These blooms are frequently dense enough to preclude recreational water contact for many weeks at a time. Loads of sediment and nitrogen to Missisquoi Bay are also a concern.

The concentration of phosphates has been increasing in Missisquoi Bay since around 1980. Total phosphorus concentrations in the bay increased by 79% during 1979-2009 (Figure 2), and Missisquoi Bay currently has some of the highest phosphorus concentrations measured anywhere in Lake Champlain.

The governments of Vermont and Québec have made significant efforts to reduce phosphorus loading to Missisquoi Bay from both wastewater and nonpoint sources. However, monitoring of phosphorus loading from the Missisquoi River, the bay’s largest tributary, has shown no significant decrease during 1991-2008, although a marginally significant decrease in phosphorus loading from the Pike River.

While significant work has been done to reduce the loads of phosphorus, more needs to be done in order to meet the target levels for load reduction.  The Governments of the United States and Canada support the work being done on the Missisquoi Bay watershed and encourage the acceleration of progress in reducing phosphorus loadings.