To Save a Lake, Kill its Fish: Invasive Species Threaten South Dakota Lake's Game Fish

Officials in South Dakota are considering dumping chemicals into Lake Yankton in order to kill all of the fish living within it. The move comes two years after the Missouri River flooded, resulting in some backfill into the lake, which brought with it a number of "rough fish" -- invasive species such as carp and buffalo fish.

Though yet-to-be-approved, the move would completely wipe out all fish, invasive and native, living in the lake. It would then be restocked with desirable game fish, according to the The Yankton Daily Press & Dakotan. The fish kill would be the first at Lake Yankton in more than three decades.

"For the most part, I think the handwriting's on the wall, myself," Jeff Schuckman, a fisheries biologist with the Nebraska Game and Parks Commission, told The Yankton Daily. "The lake got contaminated, and their (rough fish) numbers are going to expand and the game fish numbers will decrease. The warning signs are there."

Craig Bockholt, acting manager at the Gavins Point National Fish Hatchery -- one of the lake's overseers, said there are only a few "good species" of fish left. Invasive species such as grass carp, gizzard shad, smallmouth and largemouth buffalo, bighead carp and silver carp have overtaken the lake in the aftermath of the 2011 flood.

"It's going downhill and will continue to, in my opinion," Schuckman said. "It's a documented problem with the higher numbers after the flooding, and hopefully sooner rather than later we can get going" with the proposed fish kill. 

Only a few toxicants can legally be used for fish kills, including chlorine, rotenone and antimycin A, all of which are approved for use as a piscicide by the Environmental Protection Agency, according to a report by the Southern Regional Aquaculture Center.

Rotenone, which is sold under a variety of brand-names, effectively kills fish by suffocating them. Gizzard shad and grass carp are particularly sensitive to rotenone.

The effects of rotenone on birds that may eat fish poisoned by rotenone is negligible, as is its effect on other wildlife, according to the Arizona Game and Fish Department. The agency has published an in-depth dossier on the use of rotenone as a piscicide.

Some links have been made between rotenone use and the development of Parkinson's disease in farm workers.