Clear Lake Water Quality Improvement

The Rice Creek Watershed District has partnered with the City of Forest Lake to capture and treat polluted rainwater at the City Center before it reaches nearby Clear Lake. The City was awarded a Clean Water Fund Grant, from the Clean Water, Land, and Legacy Amendment, in the amount of $382,000 for the project with an additional $95,000 in local matching funds provided by the RCWD and the City. The total amount spent for the project was approximately $328,000.

The goals of this project were simple: 1) slow down the polluted runoff allowing dirt and other material to be deposited on site, and 2) remove excess nutrients such as phosphorous from the water to help clean up Clear Lake.

Project features include a new ditch, floodplain, iron-enhanced sand filters, tree trenches, a stormwater pond, and bioswale.
Ditch and Floodplain
The new ditch was constructed and connected to the floodplain, the area of land surrounding the ditch that consists of grasses and wildflowers. As water rises over the banks and enters the floodplain during large rainstorms, it slows down depositing dirt and other materials, preventing it from flowing to Clear Lake.
Iron-Enhanced Sand Filters
Iron-enhanced sand filters are one of the most exciting features of this project and can be found in three locations. These filters are designed to remove phosphorous from the water. Phosphorous provides “food” for plants and in high amounts causes algae blooms in Clear Lake. During rainstorms, water washes through a mixture of sand and iron, which binds to the phosphorous, preventing it from flowing into the ditch and to the lake. Two of the three filters are surrounded by rocks to ensure that the sand mixture does not leave the site. The third and largest filter runs parallel to the ditch and treats water in the floodplain during big rainstorms.

Tree Trenches

Two tree trenches were constructed to capture and treat polluted runoff from the City Center parking lot during rainstorms. The trees “drink” the water and make use of any extra nutrients, and then the water flows into a stormwater pond on the north end of the property. The stormwater pond was built to capture and slow runoff during rainstorms allowing dirt and other material to settle before flowing into the new ditch.


Lastly, a bioswale consisting of grasses was created alongside of the pond to slow and treat offsite runoff. The plants in the bioswale use the materials and nutrients left behind to grow and flourish.

The project was completed in spring of 2015. Additional information and project tours are available for residents at the City Center.

Please contact Mark Peterson, Public Works Engineering Technician, at 651-209-9729 for more project information or to schedule a tour.