CHARLESTON, W.Va. (AP) — State regulators in West Virginia have ordered Argus Energy to repair a water treatment system at a Lincoln County mine site after a blackwater spill killed fish.

The Department of Environmental Protection said Wednesday that the fish kill was discovered Tuesday along about a quarter-mile of Copley Trace Branch. The DEP issued a notice of violation to Argus for the spill on Monday.

The agency says deoxygenated water entered the stream after a treatment pond malfunctioned. The extent of the fish kill is still being assessed.

The DEP ordered the company to bypass the treatment pond until the system is repaired.

Argus' parent company, Debord, Ky.-based Booth Energy, didn't immediately respond to a request for comment.