Sauk Lake - Nutrients: TMDL Project

The Sauk Lake North and South Bay watersheds drains portions of four counties (Douglas, Pope, Stearns, and Todd) in the Upper Mississippi River Basin.

The outflow from Sauk Lake-North Bay goes into Sauk-Southwest Bay. The outflow from Sauk Lake (Southwest Bay) goes into the Sauk River, which flows southeast towards the town of Melrose. Upstream, the Sauk River drains 557 km2 and runs through four lakes between Lake Osakis and Sauk Lake (North Bay), which have a buffering influence on the water quality of the river entering Sauk Lake (Southwest Bay). The sub-watersheds of Sauk Lake-North and Southwest Bay are dominated by agricultural use; primarily corn, soybeans, alfalfa, pasture and animal husbandry.

In 2004, Sauk Lake was placed on the list of impaired waters after being identified as impaired by excessive nutrients. In 2008, after different water quality standards were set for deep and shallow lakes, it was decided to split Sauk Lake into two bodies of water separated by State Highway 71, which crosses a natural narrow. For the upstream and larger lake, Sauk Lake (North Bay), classified as a deep lake, the MPCA completed a TMDL report in 2013, which was approved by the EPA, also in 2013 (MPCA 2013). A second TMDL for Sauk Lake (Southwest Bay), which is classified as a shallow Lake was completed in 2016, and approved by EPA in 2017.

Map and location

Sauk Lake is located in the Sauk River watershed, which lies in the southwestern portion of the Upper Mississippi basin.

TMDL report and implementation plan

The total phosphorus loading to Sauk Lake-North Bay will need to be reduced by 36 percent to achieve the lake water quality goal of 38μg/l (reduced from the standard of 40mg/l to accommodate a margin of safety). This reduction is attained by reducing contributions from internal loading, local watershed runoff, and the main tributary, Sauk River. The TP loading to Sauk Lake (Southwest Bay) will need to be reduced by 41% to achieve the lake water quality goal of 56μg/l, which will meet the 60ug/l standard and include an explicit Margin of Safety of 7%. This reduction is attained by reducing contributions from the main tributaries, Ashley Creek and Hoboken Creek and assuming that the goals outlined in the TMDL for Sauk Lake (North Bay) (MPCA 2013) will be met. A general strategy to address the impairments is included. Non-point sources will be the focus of implementation efforts. Nonpoint contributions are not regulated and will need to proceed on a voluntary basis.


Information contact

Anna Bosch
Watershed Project Manager
MPCA Brainerd Regional Office
7678 College Rd, Suite 105, Baxter, MN 56425