The fish were discovered dead around Pierce City on Tuesday, just days after a terrible smell filled the city of Monett. The smell was believed to have been caused by the Tyson plant.
How the ammonia got into the water is what has the Department of Natural Resources investigating.
"The initial problem, of course, was Tyson’s plant had an issue over there and we had an odor issue and it was bad,” says Skip Schaller, Monett City Utilities General Manager.
The Department of Natural Resources believes the chemical "Alimet" may have been introduced into the environment via waste-water sent from Tyson’s pre-treatment system to Monett’s wastewater treatment facility.
"When that happened, the ammonia in the waste coming into the plant wasn't being treated, so we were having higher ammonia amounts going out into the stream," says Schaller. "Which fish are susceptible to ammonia, to their gills, and it was enough to be toxic to them there within a few miles stretch of the plant."
Conservationists say it was ammonia that killed thousands of fish at Clear Creek, but City Utilities workers say with every passing day those ammonia levels are going down.
The Missouri Department of Conservation is working with the Department of Natural Resources to count the number of fish killed and sort them by species and families of fish.
"What is kind of unusual about these at Clear Creek is it's a kill affecting all special and all sizes of fish," says Andy Austin, Fisheries Regional Supervisor.
Conservationists believe the ammonia has no immediate harm to humans.
As the investigation continues, Monett City Utilities is continuously testing the water to prevent something like this from happening again.
"We are working diligently with the Department of Natural Resources and Tyson to get this rectified and make sure it doesn't happen again," says Schaller.
The Department of Natural Resources is continuing to monitor the situation to determine appropriate enforcement actions.
Tyson Foods released the following statement Thursday:
"We are working cooperatively with city and state officials as they investigate this matter. We are awaiting additional details so we can understand if our operations played a role in what happened."
Copyright 2015 Nexstar Broadcasting, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.