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 aims to control nutrient levels (specifically phosphorous) in Lake Cornelia and Lake Edina.

Project Summary

The Nine Mile Creek Watershed District (District) and City of Edina are currently in the process of undertaking a multi-phased project to improve the health of Lake Cornelia and Lake Edina. To date, the projects we have implemented have included annual lake herbicide treatments by the City of Edina to control curly-leaf pondweed (2018-2020) and an in-lake aluminum (alum) treatment by the District in 2020.

Beyond the projects already implemented, the District is working with WSB and Associates to determine a goldfish and carp management strategies for the Lake Cornelia system. The District will also assess the need to improve oxygen conditions in the lake, after evaluating monitoring data.

Learn more at the individual lake pages below:

Lake Cornelia

Lake Edina

Project Goals and Objectives

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 District and City of Edina have implemented several strategies in and around Lake Cornelia to help achieve these goals.

One strategy is reducing the amount of curly-leaf pondweed, an aquatic invasive plant, in the lake through annual herbicide treatments 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

Aerial image of Rosland Park parking lot
Location of the proposed project in Rosland Park

amount of phosphorus released into the water when the invasive plant dies off and decays in mid-summer. Another strategy to improve water quality is reducing the amount of phosphorus released from the lake bottom sediments, a process called “internal loading”, by conducting an alum treatment.

To address “external” watershed-based loading from stormwater runoff, the District is designing a stormwater filtration project (discussed in the video below). This project will be constructed in the City-owned Rosland Park, and filter out phosphorus from stormwater entering Lake Cornelia. The Rosland Park Stormwater Filtration BMP is scheduled to be constructed in the fall of 2021.

Rendering of project
Rendering showing the concrete filtration vault with tiered wall planted with shrubs and flowering plants

Other management strategies under consideration to further improve water quality and the ecological health of Lake Cornelia and Lake Edina include managing goldfish and carp and improving oxygen conditions in the lake.

Goldfish and Carp 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.

Image of fish in a net on left, and man weighing goldfish at right
A sample scoop during an electrofishing survey and weighing a large goldfish on Lake Cornelia (2020)

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.

Cornelia Lake System fisheries assessment for 2020 Report

District Goldfish Study Featured on Minnesota Bound

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.

How can you help with the goldfish problem?

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.

In addition, the District needs volunteer help! Volunteers will bait fish nets with corn. The corn is designed to aggregate carp and goldfish to the nets, as other fish do not feed on the corn. Once the fish are trained to aggregate in the area, WSB will net and remove the carp or goldfish from the lake. Minimum of one week (Monday-Friday) and approximately 5-10 hours per week. Training and materials will be provided. Contact Erica if you are interested in volunteering for a week this summer.

Proposed Rosland Park Stormwater BMP Project

Watch the 20 minute video below for an overview of the proposed stormwater best management practice at Rosland Park. This proposed project aims to reduce the amount of phosphorous entering Lake Cornelia from Swimming Pool Pond and the larger watershed. The District’s engineer gave this presentation at the Public Hearing on July 15, 2020.

Curly-leaf Pondweed Herbicide Treatment

An herbicide treatment kills undesirable plants. The City Edina annually conducts herbicide treatments on Lake Cornelia that targets invasive curly-leaf pondweed.

Managing the level of curly-leaf pondweed will help protect and improve the native aquatic plant community in Lake Cornelia and reduce internal phosphorus loading.

How does an herbicide treatment work?

After a Minnesota Department of Natural Resources permit is approved, a licensed contractor applies herbicide from a treatment boat. Based on the spring plant surveys done on Lake Cornelia, an herbicide called Endothall was applied to select areas in Lake Cornelia. 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.

Endothall Factsheet

In-lake Alum Treatment

Alum Treatment Barge on Normandale Lake
Alum Treatment Barge

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.

Alum Treatment Factsheet

Studies and Reports

Lake Cornelia and Lake Edina Water Quality Improvement Project Feasibility Study/Preliminary Engineering Report

Lake Cornelia and Lake Edina Water Quality Improvement Project Feasibility Study/Preliminary Engineering Report Appendices

Lake Cornelia and Lake Edina Water Quality Study Summary_2019

Lake Cornelia and Lake Edina Water Quality Study_2019

Lake Cornelia and Lake Edina Water Quality Study Appendices

Lake Cornelia and Lake Edina Alum Feasibility Study_2019


Contact Randy, District Administrator, at 952-835-2078.