Monday, July 20, 2015

Zebra mussels confirmed in Clearwater Lake, Ruth Lake; Red River also added to infested waters list

The Minnesota Department of Natural Resources (DNR) will list three water bodies as infested with zebra mussels: Clearwater Lake in Wright and Stearns counties, Ruth Lake in Crow Wing County, and the Red River bordering northwest Minnesota. Zebra mussels likely found their way into these water bodies one of two ways, either overland or downstream spread.

Clearwater Lake and Ruth Lake were infested through overland spread, likely by people moving aquatic invasive species (AIS) attached to boats, docks and other equipment, or water not drained from watercraft. Overland spread is preventable if Minnesota's AIS laws are followed.

New infestations are usually discovered in the summer because more people are spending more time on Minnesota water bodies. The zebra mussels in Clearwater and Ruth lakes were discovered by observant people. A lake shore resident on Clearwater Lake contacted the DNR July 6 to report the discovery of a zebra mussel attached to a native mussel. A man vacationing on Ruth Lake reported that his 15-year-old son found a zebra mussel on a rock.

After these reports, DNR biologists investigated and found more zebra mussels in these lakes. In Clearwater Lake, eight zebra mussels were discovered in two locations approximately 1 mile apart. Further surveys are underway on Ruth Lake, but one additional zebra mussel was discovered on a tree branch during an initial survey.  

Zebra mussels can also move to new waterways through downstream flow. The Red River infestation illustrates this type of AIS spread. In June, researchers in North Dakota found many larval zebra mussels, called veligers, at six sites on the Red River. On July 9, Fargo city staff found an adult zebra mussel attached to a water intake on the river.

The infestation of the Red River is not surprising because the Otter Tail River in Minnesota, which flows into the Red River, has been infested with zebra mussels since 2012. Zebra mussels likely colonized the Red River by floating downstream during their early life stage when they are small and are carried by currents before they attach to hard objects.

Even though these are only the fourth and fifth inland lake infestations confirmed this year (after Eunice, Fish Trap, and Forest lakes), these reports are alarming. It is imperative that people take action and follow state AIS laws. Boaters are required by law to clean weeds and debris from their boats, drain water from their boats, bilges, and live wells, and dispose of unwanted bait in the trash. Anyone moving a dock or lift from one water body to another must leave the equipment out of the water for 21 days before placing it in the new water body.

The vast majority of Minnesota lakes, about 95 percent, are not infested by any aquatic invasive species. Likewise, the vast majority of people using Minnesota lakes follow these laws and are aware of the need to prevent the spread of AIS. As more Minnesota lakes become infested, even a small percentage of people not following the laws can result in further overland spread of these species.

More information about zebra mussels, how to inspect boats and other water-related equipment, a current list of infested waters, and how to report an infestation is available on the DNR website at

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