Officials: Cause of Huron dam fish die-off unclear

A recently completed James River dam project was the site of a massive fish die-off in Huron last week, but state officials say the cause of the deaths is unclear.

A state official says they are monitoring the situation on the ground and may restock the affected area of the river.

The fish kill was the subject of a TikTok video that was also shared on other social media platforms. In the video, a man blames the dam project for the situation and levels a series of expletives at the engineers and city leaders who designed and approved it.

A renovation of the Third Street Dam was intended to prevent human drowning in the James River, according to city officials but it has also caught hundreds of dead fish. Most of the fish were shortnose and longnose gar or silver and bighead carp.

The dam was built in 1936 to create a small reservoir for the city’s water supply. The city has since changed its water supply to ground wells and the Missouri River, but the reservoir is still used for recreation.

Although the upstream depth of the dam is only a few feet, the downstream depth at the face of the 3rd Street Dam was about 14.5 feet prior to the rock installation, according to the City of Huron. Water flowing over the dam created a strong recirculating current that pulled swimmers under the water.

Huron Police Chief Kevin VanDiepen said at least two people had drowned at the dam since he started with the department in 1988.

Stockwell Engineering, the firm contracted for the project, advised filling the dam’s downstream side with rocks to prevent swimmers from being pulled under if they go over the dam’s spillway.

About two dozen people attended a meeting in 2017 where Stockwell engineers presented the proposal and answered questions, the Huron Plainsman reported. 

That meeting included questions about the impact on fishing. Stockwell President Jon Brown said not all of the risks can be eliminated.

The Department of Agriculture and Natural Resources was aware of the modifications, according to Nick Harrington of South Dakota Game, Fish and Parks (GFP), but “Because the improvements did not alter the dam itself or the area of water impounded by the dam, no regulatory review or approval was required by the department’s Safety of Dams program.”

State: winterkill not directly related to dam

While some locals have pointed to the rocks as the cause of the fish kill, USGS streamflow data suggests that the situation may be more complicated. The flow is no less than last year, according to a streamgage located near the dam, despite the rocks being installed sometime in 2019. 

“Streamflow at the James River at Huron in the winter of 2022-2023 is fairly normal compared to the past four years, and there has not been sudden changes to the flow recently,” said USGS Hydrologist Galen Hoogestraat in an emailed statement.

Low water and lack of oxygen may have contributed to the winterkill, Harrington said in a statement.

“Low oxygen levels may stress fish, and over extended periods of time can cause mortality,” Harrington said. “Winterkills such as this can happen in lakes and streams when water levels are low and heavy snow prevents sunlight from reaching the water column.”

GFP has staff onsite to monitor the situation, Harrington said. He said GFP fisheries staff monitor winterkill through the spring, and that based on the severity and species lost, the department will make fish stocking recommendations for impacted water bodies.