Biological method of weed control

Our lake is covered with weeds. Property owners were particularly interested introducing a crayfish to our lake as means of weeds management. A question has been addressed to Jeff Forester, executive director of Minnesota Lakes and Rivers and probably the most knowledgeable person in the state about Minnesota waters,  about a crayfish introduction to control weeds. Here is Jeff’s reply:

My first impression is that it is a bad idea. What would reduce aquatic plant growth even better is to simply dye the lake blue. That shifts the light spectrum and the plants are all stunted.

Both are terrible ideas and illegal.

Lake Vermilion got rusty crawfish and they did reduce the amount of aquatic vegetation significantly. We lost our wild rice beds, our white and yellow water lilies etc. Which meant we have lost many of our ducks.  We have lost fish habitat. Crawfish also eat fish eggs, so natural reproduction of walleye is way down. Bass, which defend their nests, are up. They rusty crawfish are found at all depths. There is no way to trap them out.

There are better strategies. Common causes of increased weed growth are warmer water temperatures and nutrient loading. Leech Lake is using Lessard Sams Outdoor Heritage Funds and setting up conservation easements along the streams and shorelines feeding Leech Lake in order to protect the forest cover. Shaded streams and shorelines are cooler. There may be increased nitrogen and phosphorus runoff. This will boost weed growth. Fixing septic systems and establishing storm water retention ponds can help as I am assuming that you do not have a lot of agriculture in that area.

Before folks start dumping crawfish into the lake, maybe take a run at doing a lake management plan.”

Here how invasive red swampy crayfish looks:

Here is another “weed eater” – rusty crayfish:

If you spot those creatures in our lake, please contact DNR.





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