Lake Marion in Lakeville is a very popular summer destination. Visitors come from all over Dakota County and beyond to fish, boat, and swim during the summer months. While Lake Marion is not currently impaired for nutrients, the levels of phosphorus in the lake are close to water quality standards and could increase as more phosphorus enters the lake over time. With higher levels of phosphorus, Lake Marion would be at risk of not meeting the water quality standard and could experience worsening water quality conditions.
Stormwater (water from snowmelt and rain) drains to Lake Marion from the watershed area around the lake and brings nutrients, like phosphorus, into the lake. In 2017 and 2018, Dakota County reconstructed a large portion of County Road 50 in Lakeville in the area that drains to Lake Marion. During the design phase, the City of Lakeville and the VRWJPO worked with the County to design a practice that would provide additional phosphorus treatment to drainage from the road and from upstream neighborhoods to help protect the lake from phosphorus-laden stormwater and excess algae growth.
A combination of a pre-treatment basin, vegetated swale and an iron-enhanced sand filter was constructed. The combination of practices is extremely effective at removing phosphorus.
By constructing this practice, the City, County, and VRWJPO are helping protect Lake Marion by reducing phosphorus loading to the lake by nearly 20 pounds per year.
The project was completed cooperatively by the:
- City of Lakeville: $5,000 cash match
- Vermillion River Watershed Joint Powers Organization: $30,000 cash match and design assistance
- Dakota County: Design assistance and construction oversight
- Clean Water Fund Grant: $127,500 grant
Note: Project funding listed subject to change based on final construction costs and billing
Project photos can be found here.