Iowa Department of Natural Resources officials are trying to track down what killed over 300 fish in a Cedar Rapids stream.

The Department says Monday that a fisherman contacted DNR staff Saturday morning to report dead trout floating downstream in McLoud Run. The angler said he first saw the dead fish Friday night.

Staff later found 319 brown, rainbow and brook trout that had died. They didn't find any dead minnows or other small fish.

Officials searched the stream Saturday afternoon and Monday morning but were unable to find a pollutant. Water testing results were also inconclusive. DNR officials continue to investigate the mile-long affected area.

McLoud Run flows along the east side of Interstate 380 in Cedar Rapids, and DNR staff periodically stock the stream with trout.