Lake Pepin and Mississippi River Eutrophication Total Maximum Daily Load Report

The Lake Pepin TMDL effort began in 2002, when the State placed the lake on the impaired waters list for excess nutrients. The MPCA and partners developed a water quality model to evaluate Upper Mississippi River sediment and nutrients from Lock and Dam 1 (Ford Parkway, Minneapolis, Minnesota) through Lock and Dam 4 (Alma, Wisconsin) below Lake Pepin. Once developed, the model was applied to support TMDLs to address the Total Suspended Solids (TSS) and nutrient impairments in Pools 2, 3, and 4 of the Upper Mississippi River. Mississippi River Pools are named in accordance with the designation of the Lock and Dam at their downstream boundary. Thus, Pool 2 extends from Lock and Dam 1 (Minneapolis) to Lock and Dam 2 (Hastings, Minnesota), Pool 3 extends from Lock and Dam 2 (Hastings, Minnesota) to Lock and Dam 3 (Welch, Minnesota), etc. After the model was completed in 2009, the MPCA put the issues of turbidity and eutrophication on separate tracks, starting with the development of site-specific standards, to be followed by TMDL documents. The TMDLs addressed in this report need to be considered in a statewide watershed context. For Lake Pepin to meet its standards, phosphorus loads from upstream watersheds must be reduced. During high flows, sediment is the primary concern. The Lake Pepin Watershed includes a number of sediment reduction goals at various scales including the South Metro TSS TMDL, the Minnesota River TSS TMDL, and numerous major watershed scale TSS TMDLs. Reducing algae during low flow conditions is the primary concern and the regulatory focus of the Lake Pepin and river eutrophication TMDLs. Meeting TSS and nutrient targets for the Cannon, Minnesota, Crow, and St. Croix rivers along with reductions in the Twin Cities Metropolitan Area will contribute to the achievement of water quality goals in Pool 2 and downstream through Lake Pepin during all flow conditions. Significant progress has already been made. Municipal and industrial wastewater dischargers in the Lake Pepin Watershed have accomplished dramatic phosphorus load reductions over the past 15 years. Many wastewater facilities are already meeting their targets for local resources and Lake Pepin.