Twin and Ryan Lakes - Excess Nutrients: TMDL Project

This Total Maximum Daily Load (TMDL) study addresses a nutrient impairment in the Twin Lake chain of lakes. The goal of this TMDL is to quantify the pollutant reductions needed to meet state water quality standards for nutrients in South Twin, Middle Twin, North Twin, and Ryan lakes.

The Twin Lake chain of lakes is a regional water resource located in Hennepin County in the Shingle Creek watershed, specifically in the cities of Brooklyn Center, Crystal, Minneapolis, and Robbinsdale. The lakes are highly used recreational water bodies that support fishing and swimming as well as providing other aesthetic values. The drainage area to the lake chain is 5,550 acres of fully developed urban and suburban land. The lakes are connected to each other by channels of varying lengths. The lake system discharges into Shingle Creek, which ultimately discharges into the Mississippi River. Water quality in North and South Twin Lake is considered poor with frequent algal blooms while Ryan and Middle Twin Lake have more moderately degraded water quality. North and South Twin Lakes do not currently support recreational activities while Ryan and Middle Twin lakes partially support recreational activities.

Monitoring data in the Twin Lake chain of lakes suggest that the chain is a highly productive system, with the greatest water quality problems occurring in North Twin Lake. North Twin Lake, the uppermost lake in the chain, is a hypereutrophic lake where both internal and watershed loading appear to be significant sources of phosphorous. The majority of phosphorous in Middle Twin Lake is from water coming from North Twin Lake and from the watershed. South Twin Lake is a eutrophic lake where internal loading has the potential to increase algal productivity throughout the season. Ryan Lake, the last lake in the chain, is a deep, mesotrophic lake that has relatively good water quality for an urban lake.

Wasteload and load allocations to meet state standards indicate that nutrient load reductions ranging from 0% to 76% would be required to consistently meet standards under average precipitation conditions. North Twin contributes a substantial load downstream to the other lakes, thus improvements to that lake should result in improvement to the lower lakes in the chain. A wetland just upstream of the lake (DNR wetland 639W) was found in previous study to export a significant phosphorus load. Improvements to wetland 639W, internal load management, and reduction of nonpoint sources of phosphorus in the watershed by retrofitting BMPs would have the most impact on reducing phosphorus load and improving water quality in the chain of lakes.

Map and location

Twin and Ryan Lakes are located in the Twin Cities metro area in Hennepin County in the Mississippi River - Twin Cities watershed of the Upper Mississippi River basin.

PDF icon Upper Mississippi River Basin - Twin Cities Metropolitan Area - map

 

TMDL report and implementation plan

Links

Information contact

Rachel Olmanson
Minnesota Pollution Control Agency
520 Lafayette Road N
St. Paul, MN 55155
651-757-2473
rachel.olmanson@state.mn.us