Alimagnet Lake in Burnsville is a great place to float a canoe on a calm summer day, but not so fun when the lake is full of stinky green algae. Nutrients in stormwater runoff feed algae growth in many lakes and rivers – including Alimagnet.

Alimagnet Lake has too much of the nutrient phosphorus, which is often the key ingredient for excess algae growth. The City of Burnsville and the VRWJPO identified an area draining to the lake that was contributing a large amount of phosphorus and developed a project that would help address the issue. An area next to a stormwater pond was retrofitted with an iron-enhanced sand filter to treat water before it drained to Alimagnet Lake.

Iron-enhanced sand filters remove larger amounts of phosphorus compared to other more commonly used practices. Iron filings mixed with sand treat both dissolved phosphorus and particulate-bound phosphorus, unlike more commonly used practices that focus on capturing only particulate-bound phosphorus. This project will prevent 26 pounds of phosphorus from reaching the lake each year.

The reduced phosphorus in the stormwater that is draining to the lake will result not only in improved water quality in Alimagnet Lake, but also improved water quality in water bodies that the lake drains to, such as East Lake in Lakeville. The reduction in phosphorus aids in meeting State water quality standards and works toward removing the lake from the impaired waters list, and the VRWJPO will continue working with partners to further reduce phosphorus reaching the lake. The project also takes steps to restore and protect water resources for public use.

The project was completed cooperatively by:

  • City of Burnsville: $40,280 cash and engineering match, construction administration, and oversight
  • Vermillion River Watershed Joint Powers Organization: $29,454 cash and engineering match
  • Clean Water Fund Grant: $93,899 grant

Photos of the project can be found here.