Hundreds of small fish have been found dead after thousands of gallons of raw sewage was accidentally released into a waterway in the far eastern part of Jefferson County.

Brush Run is a small stream—less than a foot deep in most areas—that feeds into Floyds Fork. The sewage release affected half of a mile of it, and killed about a thousand one to two-inch fish.

Metropolitan Sewer District Regulatory Services Director Brian Bingham says a grease buildup caused a sewage pumping station to malfunction.

“We had just done preventive maintenance on that pump station the week before,” he said. “It’s something that was noted as a problem that needed some additional attention. However something happened in between there that it got much worse than it had been, so we are further investigating and we will come up with a solution to keep this from happening again.”

Bingham says MSD still isn’t sure how much sewage was released.

“We actually reported that it was about 10,000 gallons,” he said. “Since then, we’ve done some more detailed calculations, we really think it was between 4,000 and 5,000 gallons. But it was a very small stream so even that amount could have a substantial impact.”

The sewage overflow happened at a time when streams all over the area are already dry-and therefore stressed—because of a lack of rain. There have been at least six fish kills over the past two weeks, and the previous five were caused by the weather.

The sewage spill was reported to the Kentucky Division of Water, and regulators are considering whether to levy fines for the incident.