US Army Corps of Engineers
Omaha District

2014 Lake Yankton Sport Fisheries Restoration

Questions and Answers about the lake’s drawdown and restoring sport fish to Lake Yankton.

Published Aug. 20, 2014

Why does Lake Yankton need a fisheries restoration?

The fisheries restoration in Lake Yankton is in response to the lake becoming inundated with undesirable rough, or non-game fish. Water normally flows from Lake Yankton into the Missouri River. However, in 2011, floodwater from the Missouri River back flowed into Lake Yankton. With the back flow came a number of undesirable fish species that were not previously in Lake Yankton, or were too few to impact the sports fish already in the lake. The undesirable fish species includes carp (including Asian carp), buffalo, shad, gar, and drum. Undesirable fish drive out sports fish, destroy necessary aquatic vegetation, and diminish water quality.

What happens during a fisheries renovation?

A fisheries renovation is designed to restore balance to a lake overrun with undesirable fish. During a renovation, all the fish in a lake are killed with a chemical. Once the chemical has dissipated from the water the lake is restocked with desirable sport fish.


How was it determined there were too many undesirable fish in the lake?

Nebraska Game and Parks Commission fisheries biologists conducted surveys in 2013 and in 2014. The quantities in each survey showed the undesirable fish had substantially increased while the desirable sport fish had significantly decreased.


When will the Lake Yankton drawdown begin, and how is it done?

The Lake Yankton drawdown began in mid- August by releasing water through the control structure, known as the “Bubble”, on the southeast side of the lake near Chief White Crane Campground. Water cannot be “stopped” from entering into Lake Yankton. Natural springs, a creek, and relief wells under the embankment of the dam constantly provide water to the lake. Removing “stop logs” and opening a slide gate on the control structure allows water to flow from the lake into the Missouri River.

The lake will decrease by .15 to .25 feet a day. It will take approximately 25 days to draw the lake down a depth of 4 feet, required for the restoration.

The drawdown began during the project’s public comment period due to the time required to lower the lake. However, the chemical application will only occur once approval is given.


Will the drawdown impact recreation around Lake Yankton?

The impact of the drawdown should be minimal. Lake Yankton Beach will see the most impact. Buoy lines will be out of the water. Anyone swimming in the lake should use caution. Boat ramps should still be accessible. Camping will not be affected.


How long after the drawdown will renovation begin?

Immediately. The target date for the renovation is Wednesday, Sept. 10.


What chemicals will be used? How will they be distributed?

Rotenone is the chemical that will be used to eradicate the fish in Lake Yankton. It is the most common chemical used to treat lakes to help restore traditional sports fisheries.

Rotenone is a selective pesticide meaning the concentrations used by fisheries biologists will kill fish but not other animals.

The NGPC will use drip stations to distribute the chemical at any inlets (streams, springs, etc). They will then use pumps on boats to cover the entire lake with the chemical. NGPC completes numerous restorations each year totaling nearly 60 in the last 10 years. A Department of Agriculture pesticide application certificate is required to use the chemical.

For a fact sheet on Rotenone and its use, visit the Oregon Department of Fish and Wildlife website at:
http://www.dfw.state.or.us/fish/local_fisheries/diamond_lake/FAQs.asp


How quickly will the fish be affected after Rotenone enters the lake?

How fast fish begin to die will depend on water temperature. Some smaller fish may begin to die immediately. For others, it may take an hour or longer. It also takes time to distribute the chemical in a lake the size of Lake Yankton. Drip stations will be set up for 12 hours. It will take up to 5 hours to apply the chemical throughout the lake by boat. The application will cover the entire lake. Leaving any part of the lake untreated, could allow fish to hide in untreated water protecting them from the chemical. Careful deployment will ensure a successful renovation. Treatments are generally 99 to 100 percent effective.


Will all species of fish be affected by the chemical?

Yes. Although Lake Yankton’s size presents a challenge, biologists anticipate 100 percent eradication of the fish.


When the renovation begins, how will you stop water flowing from Lake Yankton into the Missouri River?

The USACE has conducted two control structure tests in preparation for the drawdown. A 1-foot drawdown was tested each time. When the stop logs were placed and slide gate closed, no water leaked into the Missouri River. The tests showed that once the fish kill begins the chemical should not flow from Lake Yankton into the Missouri River.


Does Rotenone affect other animals? What if other animals eat the fish?

Because Rotenone is a selective pesticide, it does not affect other animals. Other aquatic animals, birds, mammals, and insects have natural enzymes that help to detoxify the chemical. If other animals drink the water or eat the dead fish they will not be affected.


Will access to Lake Yankton be restricted during the renovation?

Yes. The public is welcome to watch the renovation from parks around Lake Yankton during the renovation process. However, once the renovation begins on Wednesday, Sept. 10, no one will be allowed in the lake or lake bed. Boat ramps will be closed. People and pets will be prohibited from entering the water or the lake bed until the chemical has dissipated.


How long will the chemical last?

How long the chemical lasts depends on sunlight and water temperature. The chemical generally dissipates within a week. NGPC employees will monitor lake toxicity and only begin restocking fish to the area once the Rotenone has dissipated to approved levels, no longer toxic to fish.


What happens to the fish? Are they removed? Will there be an odor or stench?

Most of the dead fish will rise to the surface. As they decompose, they will sink to the lake bottom or wash onto the shoreline. There are no plans to remove the fish, which will likely cause a stench. Though unpleasant, the decaying fish will restore nutrients to the lake and help restore its health.


While the lake level is down, will any habitat work be done?

None is planned. The Lake Yankton renovation is designed to help restart the fisheries.


When will water levels rise again?

Lake Yankton’s water levels will begin to rise once the stop logs are replaced and the slide gate is closed. It will rise slower than it went down, increasing about .10 feet per day. It will take about 44 days to return to normal levels.


Will you try to remove any fish prior to the renovation?

The South Dakota Game, Fish and Parks has begun a trap-and-transfer program to move game fish to other locations. South Dakota will liberalize fishing from Friday, Aug. 22 through Tuesday, Sept. 9. Nebraska will liberalize fishing from Wednesday, Aug. 20 through Monday, Sept. 8.


What is the plan for restocking the lake?

The NGPC is in charge of the restoration and restocking. They have fish stock ready at the Valentine State Fish Hatchery for the Lake Yankton project. They will begin restocking as soon as lake water quality is suitable for stocking; usually a week or two after the restoration begins. Large-mouth bass and bluegill will be stocked this fall. In the spring, NGPC plans to add black crappie, walleye, and channel catfish. Those are the only species that will be restocked in the lake.

After the initial restocking, the plan is to conduct annual stocking of walleye and semiannual stocking of channel catfish.


When will the sport fisheries be restored?

Fish stocked in Lake Yankton will have a tremendous growth rate because of reduced competition and the improved overall health of the lake. The best growth rates for fish are when they have a “fresh” system to grow in. By the fall of 2015, largemouth bass should be in the 9-inch range with bluegill being nearly 5-6 inches. By the fall of 2016, 12-inch bass should be common.


For more information, please contact:

U.S. Army Corps of Engineers at 402-667-2546,

Visit the Lewis and Clark Visitor Center

Or contact the

Nebraska Game and Parks Commission at 402-370-3374