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Common Pond Concerns
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The primary purpose of your pond is to collect stormwater runoff, but homeowners are often concerned about the appearance of their pond. Below is a description of common pond issues and their causes.
Common Concern #1: Pond is Weedy
What you see as weeds may be part of a normal pond environment. Native aquatic plants are essential to pond health. Plants provide food and shelter for wildlife such as birds and fish. Plants also absorb excess nutrients from the water and prevent shoreline erosion. Knowing what a healthy pond looks like can help adjust your expectations for your pond’s appearance.

Sometimes, invasive plants may be a problem. If one plant seems to be taking over your pond, try to identify what it is.

Check out the Minnesota Department of Natural Resources (DNR) guide to invasive aquatic plants.

Common Concern #2:  Pond is Green

If tiny green plants are floating on the surface, you probably have duckweed These are tiny native plants that provide food and shelter for wildlife. If you have floating mats of green blobs or fuzzy strings, you may have filamentous algae. If the water itself is green, it’s probably microscopic plankton algaeHaving some algae is normal, but too much algae reduces water clarity, which upsets plant growth and the natural food chain.

The best way to reduce algae is to reduce the amount of phosphorus and other nutrients entering your pond. See the information on “Keeping Your Pond Healthy.” The DNR regulates the control of algae and aquatic plants such as duckweed. Visit their website for more information about aquatic plant regulations.

Common Concern #3:  Dead Fish

Most fish kills are reported in early spring, after ice-out. During winter, ice and snow limit the amount of sunlight reaching aquatic plants, which reduces photosynthesis and oxygen production. Low levels of oxygen cause some fish to suffocate. Something similar can happen in summer after an algae bloom and subsequent die-off. Decomposition of the algae uses up oxygen, making less available for fish.

Toxins and disease also kill fish. If you see a large number of dead fish and you don’t think it’s related to a winter fish kill, report it to the City Natural Resources Staff at 952-895-4550.

Common Concern #4:  Smelly Pond
Smells from a pond are usually caused by plant decomposition. An algae bloom and subsequent die-off is often the culprit. The best way to prevent future smelly problems is to prevent algae blooms. This is best done by reducing the amount of phosphorus and other nutrients entering your pond. For ideas, see Protecting Ponds and Lakes.


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