Over 1,000 fish died in Arkansas’ Mill Creek, an estuary of the Arkansas River, prompting the Arkansas Game and Fish Commission (AGFC) to investigate.

Witnesses discovered the dead fish at the section of the creek near Riverfront Drive and P Street in Fort Smith, Arkansas, 40/29 News reported Wednesday. That part of the creek is where a local sewage treatment plant empties treated wastewater before the creek connects with the Arkansas River.

The creek was full of dead fish at one point, according to residents who spoke with the outlet.

.@ARGameandFish investigating fish kill in #Arkansas River tributary in Ft. Smith. Hundreds of dead fish found in Mill Creek, @4029news reportshttps://t.co/SNNslab9e3

— Rich Shumate (@The_Shumater) September 6, 2023

AGFC officials ruled out algal blooms, which can cause the water to lose oxygen and subsequently kill fish, because the creek is connected to the Arkansas River and actively flowing. Moving water makes oxygen loss less likely, the AGFC’s Ethan Angel told the outlet.

Still, the AGFC is actively investigating the die-off. When a mass casualty event such as this one occurs, “especially in a public waterway, [they] have to do something about it,” Angel added.

Angel also noted the Arkansas Department of Environmental Quality will test the water. “Biologists will come down, they’ll do a fish kill count,” he told the outlet. (RELATED: Scientists Discover Fish Swimming At Deepest Level Ever Recorded)

Town officials in Fort Smith said there have been no recent issues with the nearby sewage treatment plant.

“I am 100 percent confident that this is not the culprit, that the P Street treatment plant did not have anything to do with the fish kill,” Fort Smith’s water and utilities director Lance McAvoy said.

The Daily Caller reached out to the town of Fort Smith and the AGFC for comment but did not hear back from either by the time of publication.