The Iowa DNR is investigating a northeast Iowa fish kill near West Union.
The DNR says it got a report of dead brown trout below a stormwater drain that flows into Otter Creek and found the fish kill extended at least one mile downstream.
The DNR says it appears only the naturally reproducing trout are impacted — with the fish ranging from two to 16 inches. Fisheries staff say the trout are more sensitive to temperature changes and chemicals.
The report came in around 3 p.m. Wednesday and initial tests have not pointed investigators to any particular source of the kill.