Lake Cornelia and Lake Edina are shallow lakes with poor water quality that are on the state’s impaired waters list for excess nutrients. The Nine Mile Creek Watershed District is working to control nutrient levels (specifically phosphorous) in Lake Cornelia and Lake Edina.
The goals of the Lake Cornelia and Lake Edina Project are to improve water quality and the ecological health of Lake Cornelia and downstream Lake Edina.
The Nine Mile Creek Watershed District (District) and City of Edina are completing a multi-phased project to improve the health of Lake Cornelia and Lake Edina. To address pollutants in the lakes from stormwater runoff, the District installed a filtration vault located in Rosland Park in late 2021. Annual lake herbicide treatments by the City of Edina to control curly-leaf pondweed (2018-2020) have also been implemented and an in-lake aluminum (alum) treatment was conducted by the District in 2020. Beyond this, the District is working with WSB and Associates to manage goldfish in the Lake Cornelia system. The District will also assess the need to improve oxygen conditions in the lake, after evaluating monitoring data. Learn more about these project components below.
Learn more at about Lake Cornelia and Lake Edina at:
Rosland Park Stormwater Filtration BMP Project
To address pollutants coming into the lake from the wider watershed, the District installed a stormwater filtration vault in Rosland Park. It will filter out phosphorus from stormwater entering Lake Cornelia.
The project will reduce the amount of phosphorous entering Lake Cornelia from the pond to the northeast, and the larger 410-acre urban subwatershed that drains to the lake (including Southdale Mall). Water is diverted from the pond through the filtration vault, after which the water will flow to Lake Cornelia. We are testing different types of filter media in the filtration vault to see which one removes the most phosphorous from the water.
Visitors to the park can look down through the grates on top to see water flowing through the different media types. The smaller cells close to the volleyball court contain anthracite, which functions as a pre-treatment. After flowing down through the anthracite, water then goes up through one of three different media in the bigger cells. These three big cells contain either iron-enhanced granite sand, iron-enhanced aggregate, or granite sand with alumina. Filtered water then flows out through the spouts on the parking lot side, and through pipes to Lake Cornelia.
Though the water is cleaner, it is not treated for drinking. Do not drink the water from these spouts or allow pets to drink the water from these spouts.
In addition, during drier periods when water levels in the pond are too low, water from Lake Cornelia itself will be filtered through the vault. This allows us to get more phosphorous and nutrients out, even when water levels are low.
This project was supported by the University of Minnesota Water Resources Center through an appropriation from the Clean Water Fund established by Minnesota Clean Water Land and Legacy Amendment and from the Minnesota Stormwater Research Council.
For more information about the Center and the Council, visit https://www.wrc.umn.edu/projects/storm-waste-water.
For more information about the Minnesota Clean Water, Land and Legacy Amendment, visit https://www.legacy.mn.gov/about-funds.
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the Water Resources Center or Minnesota Stormwater Research Council.
The District also received funding from Hennepin County through their Opportunity Grant program to offset capital improvement funds utilized by the District to implement the project.
Curly-leaf Pondweed Herbicide Treatment
Another strategy to improve the health of the lakes is to reduce the amount of curly-leaf pondweed, an aquatic invasive plant, in the lake through annual herbicide treatments. These herbicide treatments are being conducted by the City of Edina. Reducing the amount of the invasive plant will help protect and improve the native aquatic plant community and reduce the amount of phosphorus released into the water when the invasive plant dies off and decays in mid-summer. Herbicide treatments are done in early spring when the water temperature in the lake is generally between 50-60o F. This is when the herbicide is most effective and limits damage to native plants, which start growing later than curly-leaf pondweed.
In-lake Alum Treatment
Alum treatments help control phosphorous levels in lakes. Phosphorous is a nutrient that fuels algae growth. Trained contractors apply the alum using specialized equipment and barges; this equipment ensures the precise placement of the material in the lake. On contact with the water, the liquid alum forms a fluffy aluminum hydroxide precipitate called floc. Aluminum hydroxide (the main ingredient of common antacids like Maalox) binds with the phosphorus to form a compound that does not dissolve in water. The bound phosphorus can no longer fuel algae growth. As the floc settles to the bottom, it removes phosphorus and particles from the water, leaving the lake clearer. The floc then forms a thin layer on the bottom of the lake, and binds with phosphorus in the sediment. The result is a reduction in the frequency and intensity of nuisance algal blooms.
HAB Aquatic Solutions applied alum at Lake Cornelia on May 21, 2020.
Goldfish and Carp Management
To help improve water quality and the ecological health of Lake Cornelia and Lake Edina, the District is undertaking goldfish management.
Goldfish and carp are an invasive species of fish that cause water quality problems due to their bottom feeding behavior. They stir up lake bottom sediments, reducing water clarity and releasing phosphorus. They also uproot aquatic vegetation, destroying habitat for waterfowl and aquatic communities.
The goldfish population was likely started with the release of pet goldfish into one or more of the lakes within the system. Awareness and public education are needed to prevent this from happening in any small ponds that could perpetuate the invasive goldfish population in the Cornelia chain.
A 2018 fish summary indicated that while there were carp in the Lake Cornelia system, they were not abundant. Goldfish, on the other hand, were plentiful and at a level where management of the population is recommended for water quality purposes.
A follow-up goldfish and carp study was completed in 2020 to assess goldfish and carp levels, track inter-waterbody movement through the Lake Cornelia system and test management/removal methods. Surveyors found a large number of young of the year goldfish in the lake, indicating successful goldfish recruitment (survival to the juvenile stage).
The District will continue to study the goldfish and carp in in the Lake Cornelia system in 2021-2022, to determine the best methods for goldfish management.
The District received grant funding for the goldfish studies on Lake Cornelia from the Minnesota Board of Water and Soil Resources through the Clean Water, Land and Legacy Amendment and from Hennepin County through their Aquatic Invasive Species Prevention program.
Cornelia Lake System fisheries assessment for 2020 Report
District Goldfish Study Featured
In this Minnesota Bound episode (filmed in 2020) you can see the goldfish research team in action starting at around 1:20, as they collect information on goldfish in the Lake Cornelia system in Edina.
The City of Edina takes a look at water quality in Lake Cornelia and goldfish in this featured video.
How can you help Lake Cornelia and Lake Edina?
If you have unwanted aquarium fish or plants, never dump them in a lake, creek or pond. Always surrender them at a re-home event.
You can also Adopt a Drain to keep pollution from entering the water in the first place. Learn more at mn.adopt-a-drain.org.
Studies and Reports
Visit the Lake Cornelia and Lake Edina Study page to read the lake water quality study and feasibility reports.
Rosland Park BMP Presentation (11/18/2020)
Rosland Park BMP Presentation (6/3/2021)
Contact Randy, District Administrator, at 952-835-2078.