Minnetonka
Project Overview:
Lake Holiday is a small, shallow lake surrounded primarily by residential properties in Minnetonka. Recent lake studies conducted by the Nine Mile Creek Watershed District (NMCWD) found that the lake does not meet state water quality standards due to elevated phosphorus levels, which contribute to algae growth and reduced water quality.
In December 2023, the NMCWD Board of Managers ordered the Holiday, Wing, and Rose Lakes Improvement Project to reduce phosphorus levels and improve overall lake health.
Why This Project is Needed:
District studies found that phosphorus enters Lake Holiday from several sources, including lake bottom sediments and decaying curly-leaf pondweed, an invasive aquatic plant. Elevated phosphorus levels fuel excessive algae growth, reducing water clarity and impacting the lake’s ecological health.
To address these issues, the district developed a comprehensive lake management approach that combines in-lake treatments, aquatic plant management, aeration, and watershed-based practices.
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:
Aluminum and iron treatment
District water quality studies revealed that a lot of the phosphorus in Lake Holiday s coming from the lake bottom sediments. Adding aluminum into the lake will help chemically trap that phosphorus. Since Lake Holiday’s phosphorus is traced to a lot of organic matter, iron is included in these lake treatments to help increase the treatment effectiveness.
Aeration system installation
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. In addition, these systems can help prevent fish kills
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
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.
Project Updates:
Spring of 2026, the aeration system was turned on after ice out.
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:
- August 2022: Water quality study complete
- December 2023: Feasibility study complete
- December 2023: Project ordered by the Nine Mile Creek board of managers
- 2024 and beyond: Monitoring and evaluation
- April 16, 2024 first dose of of herbicide treatment for curly leaf pondweed completed
- October 2024: Aluminum and iron treatment completed
- October 2024: Aeration system installation completed
- November 2024: Calcis treatment completed
- 2024: Water Quality Monitoring Report 2024: Holiday Lake
- May 2025: second dose of herbicide for curly lead pondweed completed
Resources:
Holiday, Wing, and Rose Lake Studies
Questions?
Contact Jordan Wein, Water Resources Project Manager, at 952-800-8307 jwein@ninemilecreek.org