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Why is the pond in my backyard green?

Post Date:01/01/2020

The most common reason a pond turns green is due to excessive nutrients which create a perfect environment for aquatic plants like algae, duckweed, and watermeal to grow. While it may not be aesthetically pleasing, aquatic plants are normal and not necessarily bad. If ponds are doing their job as designed and  capturing pollution, they can often be unsightly and covered with an over abundance of aquatic plants. 

The City of Savage has close to 300 man-made storm water ponds that serve an important function in the city’s surface water infrastructure. These ponds help to control flooding, manage the volume of water directed to our creeks and streams, and improve water quality by removing pollutants like salt, sand, fertilizers, grass clippings, and even pet waste before reaching those waters.  

“Unfortunately, our love affair with plush, green lawns is a big reason why our ponds turn smelly and green in July and August,” says Water Resource Manager Jesse Carlson. “The same stuff that makes your grass green also makes the aquatic plants grow.” Aquatic plants thrive in environments that are rich in nitrogen and phosphorous which are commonly found in lawn care products such as fertilizers and pesticides, lawn clippings, oil and grease, or animal debris and waste. When these materials run into the pond during storms, they can cause plant and algae growth. Here are a few easy things you can do to help reduce aquatic plants in your pond and promote an attractive, healthy storm water pond: 

  1. Limit the use of fertilizers and pesticides near ponds. 
  2. Pick up and dispose of pet waste. 
  3. Keep grass clippings and leaves out of ponds. As grass and leaves decompose, they produce phosphorus which can cause aquatic plant growth.
  4. Do not mow down to the water’s edge. Instead leave a buffer of native plants to trap and clean runoff and add wildlife habitat.
  5. Plant a rain garden to slow runoff from roofs, driveways and yards. This improves lawn health and reduces the amount of runoff needing management to maintain clean lakes. 

For more information about storm water ponds, please contact Water Resource Manager Jesse Carlson at jcarlson@ci.savage.mn.us or call 952-882-2686.

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