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Looking in our Lakes

Posted: 09/12/2019

Author: Julie Anderson

Category: County Board, Departments

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There is simply no better way to learn what lurks in our lakes than to look.

Douglas County Minnesota did a lot of looking this summer.

The biggest concern is what are called aquatic invasive species (AIS). You’ve most likely heard of some of them: Eurasian watermilfoil and zebra mussels are the best known and most common in our county.

There’s also curly leaf pondweed to be concerned about, starry stonewort, which is very scary, and flowering rush which sounds pretty but it’s not.

One way the county is counting its invasive species is by using AIS funds to hire a survey team. In July, Steve McComas and his son Connor, from Blue Water Science in St. Paul, started methodically looking for species. They crisscrossed 15 lakes through the end of August. Their preliminary findings show they did not find any new areas of invasive species. They did, for the first time, document the presence of Eurasian watermilfoil in Lake Carlos which has been on the Minnesota DNR infested waters list since 2012.  Douglas County plans to have additional lakes surveyed over the next two years.

We went out with them on Lake Ida where they showed us how they use a grid of sampling points, GPS, and sonar to record their findings. Steve navigated while Connor used a long-handled rake or a throwable rake to gather up the vegetation on the bottom of the lake. At each point they recorded what they found. This grid can be replicated in the future to compare year to year. They also did what’s called meander sites which means they dropped a rake between points occasionally to see what they could find.

And, they point out, most of what they saw is high-quality native plant growth which is good for lakes. It helps the food chain which helps the fish. The problem is the invasive species are trying to overtake the same space occupied by the native plants.

For example, invasive species like flowering rush, which was just discovered on Grant Lake near Holmes City. This is a grass-like plant with pink flowers that can overtake habitat and make it difficult for boats to access open water. It’s a perennial that grows one to four feet high along shores in shallow, slow-moving water. It can also grow in deeper water and is hard to identify when it’s now flowering. Douglas County implemented its emergency response plan to take quick action following this discovery. The county worked with the Department of Natural Resources which hand pulled some of the flowering rush. An herbicide was used to treat the remaining plants. Unfortunately, during this process, the county also discovered zebra mussels in Grant Lake. The DNR also confirmed zebra mussels in multiple locations in Lake Oscar. Widespread distribution limits any feasible treatment options.

Starry stonewort is a bushy, bright green macro-algae. It has a white star-shaped bulb (technically called a bulbil) on it. In non-scientific terms, it looks like a tangled string of white Christmas lights. It can take over a lake in dense mats which prevent us from enjoying the lake where we want when we want. It also overtakes the natural habitat ultimately making the lake unsuitable for fish and animals. On August 17 volunteers in Douglas County and across the state searched lake access points for starry stonewort. There were no discoveries of starry stonewort in Douglas County.

Successfully fighting aquatic invasive species will take residents and visitors along with the county and DNR. Everyone who transports their boats from lake to lake must drain the water and thoroughly clean and dry the exterior. This includes wave runners, paddleboards, canoes, kayaks or whatever kind of floating device used. It only takes a small amount of time to make a big difference. For more information on aquatic invasive species, water quality, lake shore and Alexandria area lakes go to


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