Harmful Algal Blooms (HABs) in Lake Erie pose significant threats to the ecosystem and human health. Lake Erie is a source of drinking water for 12 million people in the U.S. and Canada, home to a $12.9 billion tourism industry and a world class fishery. HABs were largely absent from Lake Erie from the 1980s until the mid to late 1990s and have been growing steadily worse in intensity (i.e., density and surface area), with the five worst blooms on record occurring since 2011. The primary driver for the excessive algal blooms is phosphorus delivered from major rivers during spring storms.
Much of the phosphorus loading into the lake prior to 1972 was caused by point-source pollution and have been significantly reduced by permitting authorities under the Clean Water Act. Point sources of phosphorus from sewage treatment plants decreased by about 75% and permitted facilities, including combined sewer overflows (CSOs) associated with wastewater treatment plants, now contribute <8% of the phosphorus in the Maumee River Basin. Another phosphorus source, home sewage treatment systems, contributes only 4% of the total phosphorus load annually in the Maumee River.
As of January 2013, Scott’s Miracle-Gro removed phosphorus from its lawn care products, and it is estimated that 95% of the lawn care fertilizer market followed Scott’s lead, thereby reducing the potential loss of phosphorus from residential landscapes.
The Maumee and Sandusky Rivers contribute the largest tributary loads of phosphorus to Lake Erie and the Great Lakes. Approximately 88% to 93% of the phosphorus loads from these two rivers come from nonpoint sources, of which agriculture is the dominant land use (i.e., over 70% of the watershed). These tributaries do not typically deliver nutrient loads at a continuous rate throughout the season, but instead as pulses during spring storm events.
With the return of eutrophication to the lake, scientists, policymakers and stakeholders have been seeking strategies to reduce annual HABs. The U.S.-Canada binational Great Lakes Water Quality Agreement sets goals and timeframes to address excess algal growth in Lake Erie through nutrient management. New phosphorus loading targets were adopted by the states, province and federal governments in 2016.
The targets call for a 40% reductions from the Maumee River in spring loading to address the annual large Western Basin bloom and a 40% reduction in phosphorus from other rivers in the western and central basins to address local, nearshore blooms. In addition, there is a 40% reduction in annual loading from the western and central basin rivers to address the low hypoxia areas in the central basin creating a threat to fisheries and ecological health in the central basin.