Newsroom Midwest Region

Invasive water flea found in Upper Mississippi River

March 5, 2018

Invasive common water fleas collected from Pool 8 of the Upper Mississippi River near La Crosse, Wisconsin in August 2017. Photo courtesy of Elista Fisher/University of Wisconsin - La Crosse.
Invasive common water fleas collected from Pool 8 of the Upper Mississippi River near La Crosse, Wisconsin in August 2017. Photo courtesy of Elista Fisher/University of Wisconsin - La Crosse.

Working closely with biologists from the University of Wisconsin-La Crosse, we recently documented the invasive common water flea, Daphnia lumholtzi, in a new location. Two individual water fleas were identified in December 2017 from a sample collected on August 7, 2017 in a backwater of Pool 8 of the Mississippi River. The invasive water fleas, a type of zooplankton, were found during collaborative plankton monitoring efforts conducted on the Mississippi River near La Crosse, Wisconsin.

In the United States, the common water flea has thrived in warmer lakes and reservoirs in the south. However, the species was first detected in the Mississippi River during 1999 by researchers working on Lake Pepin in Minnesota.  The most recent discovery of water fleas in Wisconsin provides new evidence to suggest that the species is more widespread in the Mississippi River basin than previously thought.

Previous studies indicate that the invasive common water flea can reproduce quickly and out-compete native zooplankton. Native zooplankton are an important food source for juvenile sportfish and other fish species that consume plankton throughout their lives, like paddlefish. Unlike most native zooplankton, the common water flea has large, sharp spines on its head and tail that makes it difficult for some fish to eat. If water fleas become too abundant in an area, edible zooplankton can become less prevalent for fish to eat.  This can lead to the movement of fish out of the area, or reduced growth rates of fish that remain in waters invaded by common water flea.

The common water flea is originally from the warm lakes and streams in Africa, southern Asia, and Australia. It has been inadvertently introduced to numerous locations throughout the world. It is unclear exactly how these introductions have occurred, but scientists hypothesize that the movement of watercraft among water bodies may be a major mode of transport for common water flea. Collaborative plankton monitoring efforts on the upper Mississippi River will continue during the summer of 2018.