WEST UNION - DNR staff spent Wednesday in West Union working to track down the cause of a fish kill reported earlier that morning. They started finding dead brown trout below a stormwater drain that flows into Otter Creek. The fish kill extended at least a mile downstream. DNR field tests did not point to a definitive cause of death. It appears to have affected only the naturally reproducing trout, not other fish species which were swimming around in the creek. Dead trout ranged in size from about two to 16 inches. DNR fisheries staff said trout are more sensitive to temperature changes and chemicals. They conducted a fish count. The investigation is ongoing. Efforts will focus on identifying the source of pollutants that could have entered the creek through a storm drain. Residents reported they first saw dead fish about 3 p.m. Tuesday. DNR investigators encourage people to call in fish kills as early as possible to the 24-hour spill line at 515-725-8694. Early reporting helps DNR staff determine the pollutant source before it washes downstream.