Summary of Annex 4 targets
Priority tributaries for nearshore algal blooms. Map created by the U.S. EPA and sourced from Recommended Binational Phosphorus Targets.
The nutrient annex of the Great Lakes Water Quality Agreement (Annex 4), identified eight priority tributaries in the western and central basins of Lake Erie to focus phosphorus reduction efforts to reduce harmful algal blooms (HABs). On the U.S. side the priority tributaries are the River Raisin, Maumee River, Toussaint Creek, Portage River, Sandusky River, and Huron River. In Canada the priority tributaries are the Thames River and Leamington Tributaries.
In order to reduce HABs to an acceptable size, a target reduction of 40 percent for both soluble and total phosphorus was set for spring (March 1 through July 31) inputs compared to 2008. The 2008 base year was selected due to the quality of data and because conditions in 2008 were considered average. Attaining the target reductions is expected to result in a bloom similar to the 2012 bloom. The 2012 bloom is considered to be a mild year with no significant impacts noted.
In addition to the state and provincial efforts under Annex 4, in 2015 through the Western Basin of Lake Erie Collaborative Agreement, the governments of Michigan, Ohio, and Ontario agreed to work to achieve the reductions to the western basin by the year 2025.
Annex 4 also set an annual 40 percent reduction for both soluble and total phosphorus inputs compared to 2008 in order to reduce hypoxia (low oxygen) in the central basin of Lake Erie.
More information can be found on the Recommended Binational Phosphorus Targets page on the U.S. EPA website.