Minnetonka

About

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 Details

The District plans 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 of 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.

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 plans to do a fall 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.

Major Project Milestones

  • Water quality study complete: August 2022
  • Feasibility study complete: December_2023
  • Project ordered by watershed district: December 2023
  • Monitoring and evaluation: 2024 and beyond

Lake Holiday

  • Aluminum and iron treatment: Planned for fall 2024
  • Herbicide treatment: Planned for ice out 2024
  • Aeration system installed: Planned for fall 2024

Wing Lake

  • Aluminum and iron treatment: Planned for May 2024

Lake Rose

  • Aluminum treatment: Planned for May 2024

Sub-watershed Wide

  • Enhanced Street Sweeping: Fall 2024

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.

Resources

Holiday, Wing, and Rose Lake Studies

Questions?

Contact Erica Sniegowski, District Administrator, at 952-358-2276 esniegowski@ninemilecreek.org