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Reducing algae blooms in your local lake

Media contact: Catherine Dehdashti, U of M Extension, (612) 625-0237,

ST. PAUL, Minn. (7/31/2012) —If you notice your lake or pond is covered with mats of green or looks like "pea soup" this July or August, it may be from an algae "bloom."

"Algae blooms occur when the conditions for algae growth are optimal - these include warm temperatures, lots of sun, and abundant nutrients," said Mary Blickenderfer, University of Minnesota Extension water resources educator. "Reducing the amount of nutrients that enter the lake is one way that property owners can help reduce algae blooms. "

Phosphorus is the nutrient of most concern in Minnesota because the growth of algae in our lakes is usually controlled by how much phosphorus is available. Blickenderfer stated that under the right conditions, a single pound of phosphorus can lead to 500 lbs. of algae.

Here are some shoreland management tips that Blickenderfer says will reduce the phosphorus coming from your property:

  • Be aware that some fertilizers, leaves and grass clippings, soil, and wastewater all contain nutrients that contribute to algae growth.
  • Leave an un-mowed area between your mowed lawn and the lake to trap and filter out unwanted nutrients, preventing them from reaching the lake .
  • Dispose of leaves and clippings well away from the lake - never in the lake.
  • Maintain your septic system properly.
  • Use waterbars or berms to redirect stormwater running down paths and roads into areas of healthy vegetation that will trap and filter out unwanted nutrients.

Occasionally blue-green algae blooms can produce toxins that are harmful to fish and other animals, including cattle and pets. In Minnesota, several dogs have died from swimming in waters with blue-green algal blooms. If the water looks like pea-soup or smells swampy, it may be from blue-green algae. If you, your children, or your pets come in contact with blue-green algae, wash thoroughly as soon as possible, and keep dogs from licking the algae off their fur.

Treating lake water to reduce algae blooms requires permission from the MN Department of Natural Resources. Treating the water is usually not practical, may be expensive, and can pose risks to fish and other aquatic life. The problem may also return if the correct steps are not taken to prevent the conditions that cause the blooms.

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