Big Sioux River tributary floodwaters wash through cattle yards in the upper reaches of the river basin on April 13, 2023. (Brad Johnson/For South Dakota Searchlight)
The state of South Dakota’s lackadaisical, careless approach to protecting its lakes and streams from agricultural pollution is glaringly apparent when floods are viewed from an airplane.
Hundreds of acres of plowed fields sent tons of black soil down the Big Sioux River during the week of April 8-15. Significant amounts of mud ended up in Lake Kampeska, one of the state’s more economically important lakes.
Similar to staring down the barrel of a shotgun, Lake Kampeska absorbs much of the Big Sioux’s flood blast, and big events cause major damage.
It is cheap and easy to load the approximately 4,817-surface-acre lake with sediment and pollutants such as nitrates, phosphorus, pesticides and E. coli.
It is very expensive and virtually impossible to remove that pollution. Unfortunately, the state does not care about either end of the pollution pipeline.
To document the incoming pollution, the Lake Kampeska Water Project District conducted daily sampling of water flowing into the lake during the recent flood. Results will be released when available.
Past studies show big flood events cause major damage. Analysis by district consultant Jack Little, a retired U.S. Geological Survey hydrologist, showed the 1997 flood dumped the equivalent of all sediment contributed by river flows in the prior 50 years.
That sediment doesn’t affect the entire lake, however. A 2002 USGS study titled “Sediment Accumulation and Distribution in Lake Kampeska” reported that in the prior 50 years only 6 inches of sediment had accumulated over much of the lake. That was a different story at the lake’s mouth.
In the first 1,600 feet out from where the Big Sioux enters Lake Kampeska at state Highway 20, the study said nearly 4 feet of sediment was dumped by flood events between 1951 and 2000.
Since the study was done, Lake Kampeska experienced major flooding in 2001, 2010, 2019 and again this year.
The source of the sedimentation was clear during an airplane flight that I and former Watertown Public Opinion Publisher Mark Roby took on April 13 to document the flood. We both are Lake Kampeska Water Project District board members.
The flight covered much of the 383-square-mile watershed that feeds Lake Kampeska and Lake Pelican.
The small meandering banks that carry the Big Sioux River during much of the year were faint outlines in the expansive floodwaters. Water rushed over many exposed tilled fields, some of which went to the river’s edge. Plumes of black dirt from marginal crop land flowed into the river.
One particular farm headquarters operation had feedlots on both sides of a flooded waterway with livestock trails through the channel. Floodwaters had turned the cattle yards into mud puddles, and undoubtedly manure was headed toward Lake Kampeska and downstream.
The problem is not new, as watershed project reports have fingered the culprit for decades. Here’s an excerpt from a March 31, 2005, final report to the state and the Environmental Protection Agency on a segment of the Upper Big Sioux River Watershed Project:
The Big Sioux River meanders through a wide floodplain. Its banks are subject to extensive erosion caused by extended spring runoff and large storm events. These events carry upland and floodplain runoff from croplands and rangeland. High concentrations of nutrients and solids are carried by the Big Sioux River to both lakes [Kampeska and Pelican] from livestock feeding operations, grazing lands and row-crops. Extended livestock access to streambanks and the use of pesticides that remove plants from the river and tributary banks increase the potential for erosion.
The state’s answer to this is voluntary cooperation and reliance on federal EPA money, which is woefully inadequate. Essentially, it ignores the problem.
There are some producers in the Upper Big Sioux who have participated in conservation programs and are good stewards. But too many are not.
In recent years, the state has pushed buffer strips, but the incentives are insufficient. It is more lucrative to farm to the river’s edge and easier to plow through tributaries.
As long as our legislators and governor continue to condone agricultural pollution, our lakes and streams will continue to die.
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