Minnetonka

Background:

Holiday, Wing, and Rose Lakes are small, shallow lakes primarily amongst residential properties in Minnetonka. Recent District lake studies show poor water quality below state standards in all three lakes. The Nine Mile Creek Watershed District Board of Managers ordered the Holiday, Wing, and Rose Lakes Improvement Project in December 2023. The projects on these lakes seek to improve the water quality and specifically reduce the amount of phosphorus, an algae producing nutrient, in these lakes.

Project Updates:

Community Engagement:

A public open house was held on December 5th, 2023, at the Minnetonka Community Center. This was a drop-in event where residents could view informational posters and ask staff questions about the proposed water quality projects. Other community engagement events were held during the development of the water quality study.

Project Timeline:

Major Project Milestones

  • August 2022: Water quality study complete
  • December 2023: Feasibility study complete
  • December 2023: Project ordered by watershed district
  • 2024 and beyond: Monitoring and evaluation

Lake Holiday

  • Completed October 2024: Aluminum and iron treatment
  • First dose completed April 16th, 2024; Herbicide treatment:
  • Second treatment completed May, 2025: Herbicide treatment
  • Completed October 2024: Aeration system installed
  • Completed November 2024: Calcis treatment
  • Water Quality Monitoring Report 2024: Holiday Lake

Wing Lake

  • Completed May 2024: Aluminum and iron treatment
  • Water Quality Monitoring Report 2024: Wing Lake

Lake Rose

  • TBD in 2026: Aluminum treatment
  • Water Quality Monitoring Report 2024: Lake Rose

Sub-watershed Wide

  • Enhanced Street Sweeping on-going

Project Details:

The District completed a combination of activities in 2024 to help reduce the amount of nutrients contributing to poor water quality in the Holiday, Wing, and Rose lakes and improve overall lake health:

Lake Holiday

  • Aluminum and iron treatment
  • Aeration system installation
  • Herbicide treatment for curly-leaf pondweed
  • Enhanced street sweeping

Wing Lake

  • Aluminum and iron treatment
  • Enhanced street sweeping

Lake Rose

  • Aluminum treatment
  • Enhanced street sweeping

Project Activities Explained

Aluminum and Iron Sediment Treatment

Image of Barge applying alum to a lake
Barge applying aluminum to a lake.

District water quality studies revealed that a lot of the phosphorus in Holiday, Wing, and Rose lakes is coming from the lake bottom sediments. Adding aluminum into the lake will help chemically trap that phosphorus. When aluminum and iron are present in oxygenated water, phosphorus prefers to stick to those elements rather than be loose in the water column. This effectively traps the phosphorus so it isn’t available for algae production. Phosphorus that comes from organic matter sticks to iron better than aluminum. Since Lake Holiday and Wing Lake’s phosphorus is traced to a lot of organic matter, iron is included in these lake treatments to help increase the treatment effectiveness.

Lake Aeration

Lake Holiday has low oxygen levels. Installation of an aeration unit on Lake Holiday will increase the lake’s oxygen. Oxygen is important for the success of the aluminum and iron treatment. When oxygen is present, iron, in particular, will continue to stick to phosphorus. Aeration of Lake Holiday will prolong the effectiveness of the aluminum and iron treatment.

Herbicide Treatment for Curly-leaf Pondweed

Curly-leaf pondweed is an invasive aquatic plant that dies off mid-summer causing a large release of phosphorus in the water. Reducing the amount of the curly-leaf pondweed in Lake Holiday will help reduce the phosphorus levels in the lake and will improve the native aquatic plant community. 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. The District plans to use the herbicide, Galleon, for Lake Holiday’s treatment.

Enhanced Street Sweeping

Street sweeper collecting leaves on a residential street
Street sweeper collecting fall leaves.

On-going enhanced street sweeping is street sweeping beyond routine sweeping. Enhanced street sweeping also prioritizes sweeping where the most organic material like leaves and twigs are expected. Collecting organic material from streets before it enters the storm drains that lead to Holiday, Wing, and Rose Lakes reduces the amount of phosphorus and other pollutants entering the lakes. The City of Minnetonka is currently doing an additional fall street sweeping in the Holiday, Wing, and Rose sub-watersheds in addition to its routine spring street sweeping. In the future, the watershed district will assess if additional sweeps are needed to help reach water quality goals for the lakes, and, if needed, how to implement additional sweeps.

Resources

Holiday, Wing, and Rose Lake Studies

Questions?

Contact Jordan Wein, Water Resources Project Manager, at 952-800-8307 jwein@ninemilecreek.org