Was the Big Sioux River ranked as one of the dirtiest in the nation?

The Big Sioux River was ranked in the top 10 for the amount of toxic substances released into the watershed in 2020, according to a report by Environment America, but improvements to wastewater treatment at Smithfield Foods has improved the river’s quality.

The 2022 “Wasting Our Waterways” report ranked the Big Sioux River watershed sixth in the country for toxic substances released into the river in 2020.  The Lower Ohio-Little Pigeon watershed in Indiana and Kentucky ranked No. 1.

Smithfield Foods was a major factor in that ranking, though the amount of nitrates released  from the meat packing plant shrunk from 4.9 million pounds in 2020 to 1.1 million pounds in 2024 after the company opened a $45 million wastewater treatment facility.

Smithfield’s discharge is downstream of Falls Parks and the city’s core. Ag runoff from upstream is a bigger factor in unsafe river conditions in Sioux Falls.