PUBLIC NOTICE: Thin Ice on Moody and Shields Lake due to Winter Aeration

Thin ice on Moody and Shields Lake

The Comfort Lake – Forest Lake Watershed District is planning to run an aeration system on Moody Lake (Chisago County) and Shields Lake (Washington County) beginning on or after January 1, 2023. This will result in thin ice and/or open water on the west side of Moody Lake and west of the public fishing pier on Shields Lake. Aerators will remain on until ice-out in spring 2023. Signage will be posted around the perimeter of the thin ice and at access points around the lake. Please exercise EXTREME CAUTION on Moody and Shields Lakes from January 1st until ice-out in spring.

On many lakes, oxygen levels remain high through the winter months due to photosynthesis of underwater plants, lakebed spring inputs, or in large lakes, the sheer volume of water.  In smaller lakes like Moody and Shields Lakes, thick ice and deep snow can reduce sunlight penetration into the lake, causing decreased photosynthesis of plants.  This can lead to low oxygen levels and can cause stress or winterkill of gamefish. Healthy gamefish populations are important as they help to control black bullhead and common carp (roughfish) populations by feeding on their eggs in the spring.

Large populations of carp and bullheads can be undesirable as these species are bottom feeders that stir up lake sediment and nutrients from the lake bottom. This harms native aquatic plants and decreases water quality and clarity. Roughfish are capable of surviving in low oxygen conditions better than gamefish, which means they can outlive their predators during the winter months when the lake is frozen over. Aeration (similar to an aquarium bubbler) increases oxygen levels in the water during the winter months which can help gamefish survive and keep the roughfish populations in check. A lower population of roughfish species is expected to result in cleaner, clearer water in Moody and Shields Lakes.

Again, the aeration on Moody and Shields Lakes will cause thin ice and/or open water. Pay attention to warning signs and use EXTREME CAUTION on Moody and Shields Lakes when on the ice.  We recommend that you keep a minimum of 100 feet from all warning signs and 200 feet from any open water.  Please do not hesitate to contact the District with questions.

Funding for the CLFLWD’s watercraft inspection program is provided by multiple sources including the Aquatic Invasive Species Prevention Aid Program for both Washington and Chisago counties, local municipalities, and local interest groups. Inspectors are stationed across all five public accesses in the District. District-wide, watercraft inspectors performed 8,956 inspections and worked 3,673.75 hours in 2022. You can learn more about the District’s watercraft inspection goals in the 2022-2031 Watershed Management Plan.

Topic Contact

Garrett Miller

Aquatic Invasive Species Coordinator

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