Positive habitat trends noted after fish removal at Lake Christina

One year after the application of a fish-killing agent to Lake Christina, researchers from the Minnesota DNR, North Dakota State University and University of St. Thomas have noted positive trends in water quality and habitat conditions on the lake.

Rotenone, a chemical agent, was applied to the 4,000-acre lake in Oct. 2003 to remove fish that were decreasing water quality and aquatic vegetation abundance. Lake Christina, located in northwest Douglas County, is an important waterfowl migration habitat lake, especially for canvasbacks and other diving ducks.

The teams of researchers monitored water quality, water clarity and habitat conditions throughout the summer. Indications are that the rotenone treatment has improved water clarity and increased the abundance of aquatic plants.

"The preliminary results of fish population assessments seem to be in line with what we expected," said Tom Carlson, a DNR waterfowl habitat specialist in Fergus Falls who has been working on Lake Christina for more than 25 years. "The university and DNR fisheries researchers didn't expect the rotenone to remove 100 percent of the fish in Lake Christina, but the overall density of fish in the lake today seems to be low relative to other shallow water systems. Fish sampling yielded very few young-of-the-year fish, which is also a very good sign."

If more aquatic vegetation grows in Lake Christina it will attract more waterfowl. The area historically has been a stopover for migrating waterfowl. In addition to monitoring fish populations and water quality, the researchers are tracking waterfowl numbers and potential changes in the numbers of breeding non-game birds, such as Western grebes.

"Although the water isn't clear by most peoples' standards, we're encouraged by improvements in our Secchi depth measurements," Carlson said.

Clearer water is most likely attributed to increases in aquatic invertebrates called Daphnia, or water fleas, which now thrive in the lake.

"It's a living example of Ecology 101," Carlson said. "Daphnia eat phytoplankton, which clears up the water and allows light to penetrate enough for rooted aquatic vegetation to grow. During the 2004 plant survey, we found aquatic plants at every sample station, which is a dramatic improvement compared to the years prior to the treatment."

Based on past experience, researchers are optimistic that Lake Christina is experiencing results similar to a rotenone treatment in 1987. But this effort has a greater likelihood for long-term success.

For more information about the Lake Christina habitat improvement project, contact Nicole Hansel-Welch, DNR shallow lakes program coordinator at (218) 833-8626 or nicole.hansel-welch@dnr.state.mn.us.