The Big Platte Lake and Platte River watershed monitoring program, 1993-2012

The Clean Water Act of 1972 mandates that analyses be performed to determine allowable phosphorus loads from point and nonpoint sources that are consistent with the water quality standards. This allowable loading is called a total maximum daily load (TMDL). The purpose of this program is to monitor the lake and rivers to develop a credible TMDL for Big Platte Lake. The only significant point source of phosphorus in the watershed is the Platte River State Fish Hatchery operated by the Michigan Department of Natural Resources (MI DNR). The outflow from the Hatchery discharges into the Platte River 17 km upstream of Big Platte Lake. The maximum Hatchery phosphorus loading was estimated to be 1,960 kg/year in 1974. Today, the mean net loading from the Hatchery is only about 79 kg/year. This reduction was attained by upgrading the solids handling technology at the facility and by using low phosphorus fish feed. The Hatchery contributes approximately 3% of the total phosphorus load that enters the Lake and is currently compliant with National Pollutant Discharge Elimination System (NPDES) requirements.