SIOUX FALLS, S.D. (KELO) — The runoff from melting snow has increased the water level of the Big Sioux River and likely, the level of pollutants, said Travis Entenman, the managing director of the Friends of the Big Sioux River.

The non-profit’s mission is to “protect and restore the Big Sioux River and its watershed, improve the water quality, and educate our community to build a conservation ethic,” according to its website.

When there is rapid run off of snow melt the water will remove loose top soil or animal waste and carry it into a creek or other tributary and carry it into the Big Sioux River, said Troy Lambert, an environmental analyst for the City of Sioux Falls.

“Heavy snowmelt or heavy rain are two sides of the same coin,” Entenman said. “What we’ve found with a heavy rainfall or a large snowmelt is that we see an increase in pollutants. The Big Sioux water quality gets worse.”

Most of the pollutants in the river come from non-point sources such as run off from land. Entenman said fertilizer or other materials that were on the street or ground before snow covered them, stayed under the snow until it melted and then were carried into bodies of water.

The quality of the water in the Big Sioux River has gotten attention since at least 1973 when an Environmental Protection Agency (EPA) study cited low oxygen levels, excessive concentrations of ammoniacal nitrogen, and fecal bacteria contamination. A 2014 study by the then South Dakota DENR listed fecal coliform bacteria, total suspended solids and mercury as impairments in the Big Sioux River Watershed. In 2022, the Friends of the Big Sioux River gave the river an F for total suspended solids and levels of E. coli but an A for nitrate levels.

The Friends of the Big Sioux will start testing Big Sioux River and watershed water in May.

The city tests the river water in five spots once a week year round. The sites are: Interstate 90 where the river enters the city from the north, at Falls Park because it’s a recreational area, at Skunk Creek which is a tributary, Bahnson Avenue, east of town, before the city’s wastewater treatment plant and at Timberline or at Highway 11, after the wastewater treatment facility.

Lambert said the monitoring system was created to monitor the city’s affect on the water quality of the river.

“It’s pretty hard to draw any significant conclusions,” Lambert said of the water test results. The data provides a snapshot in time, but it can also be used to draw some general conclusions about the river’s water quality, he said. But it can’t be used for absolute conclusions on the health and quality of the river water.

Although the tests are done once a week, it could be two, three or five days between tests, he said. And tests are tied to weather conditions that existed at the time of the test but that isn’t always included in the data., Lambert said.

The tests do provide valuable information to the city. An increased level of nitrates could indicate an issue at the wastewater treatment plant or in other areas, Lambert said. The city could then investigate and do more testing, he said.

The water testing also prompted the city in 2012 to start a pet waste program for pet owners to pick up and dispose of animal waste instead of leaving it on a lawn, park or other area.

Testing indicated that the major source of E. coli in the river in the city was from pet waste, Lambert said.

“I would expect that with all the runoff there would higher levels of E. coli (in the river),” Entenman said.

The city does test for E. coli in the Big Sioux from May through October during recreation season, Lambert said.

Sioux Falls also tests for dissolved oxygen (DO), nitrates, total suspended solids (TSS), pH and biological oxygen demand (BO).

Levels of DO that are too high or low can harm aquatic life. “It’s the amount of oxygen required by fish and other aquatic life,” Lambert said of DO. “That’s a very key indicator for fish life,” he said.

April 20 tests for DO ranged from 10.12 to 12. Healthy levels are 6.5-8 mg/L. And, a dissolved oxygen level of 9-10 mg/L is considered very good. Generally, a higher dissolved oxygen reading indicates a better water quality, according to Lehigh University.

pH or, hydrogen ion concentration, in water levels were around 8 on April 20. The EPA uses a criteria of 6.5 to 9.

The tests for TSS, BOD and nitrates were last done by the city in late 2022.

TSS is the water’s clarity. If the river is muddy, the TSS level would likely be high, Lambert said.

The Friends of the Big Sioux say it uses South Dakota Department of Agriculture and Natural Resources parameters for TSS, E. Coli and nitrates. The TSS parameter is 90 mg/L, E. coli is 126 mL CFU and 10 mg/L for nitrates.

The city also tests for phosphorus. It is an essential nutrient but too high levels can harm aquatic plants and lower dissolved oxygen levels.

The BOD deals with the demand for oxygen by bacteria and microorganisms in the water. A high BOD means more oxygen is needed and the species that live in the river have less access to oxygen. That negatively impacts water quality. A low BOD means less oxygen is being used and usually means cleaner water.

Testing for nitrate levels in the river is informative but more specific for the city, it can indicate issues with a release at the city’s wastewater plant or other non-city areas, Lambert said.

Entenman and Lambert said levels of some non-point source pollution could increase in the spring as lawns get fertilized and farmers spread fertilizer on fields.

Although there is some flooding along the river, dry conditions in fields and bodies of water meant flooding like that of 2019 did not happen.

“The ground was able to absorb more water than it did in 2019,” Lambert said.

“The good thing (snow) does replace the quantity of water,” Entenman said. Ground water and surface water benefitted from the snow.

Ironically, Entenman said, the lower the water level in a dry year, the cleaner the water.