A leak from a facility in Miami caused compost liquid to go into Tar Creek.
Miami City Manager Dean Kruithof said the leak came from J-M Farms.
He said J-M Farms is working with the Oklahoma Department of Agriculture on cleanup.
State inspectors say the spill turned the creek dark for about two miles, killing thousands of fish.
Tar Creek is a superfund site that is still in the recovery process after decades of contamination from zinc and lead mining.