Results of an investigation into an August fish kill in northwest Iowa show animal manure is likely the reason dozens to hundreds of fish were found dead in the Floyd River.
Iowa’s Department of Natural Resources received final results Thursday morning that show elevated levels of ammonia and E. coli about 8 miles downstream of the kill site. Ammonia and E. coli are found in animal manure.
DNR Senior Environmental Specialist Julie Sievers says a fish kill in this area is unusual. This one affected green sunfish, stonecat and white sucker.
“Upstream of this area, there were abundant live fish visible in the tributaries so that would tell us that generally this is not an area where we’ve had repeated releases of any type of contaminant that would kill fish,” Sievers said.
Fisheries staff reported the fish were between 2 and 10 inches long and in stages of advanced decay.
Sievers says scientists found levels of contaminants near the area that they say were not high enough to kill fish. But rainfall and the flow of the river likely diluted the pollutants between the time of the kill and when officials were notified, which is estimated to be about a four-day window.
The DNR estimates numbers of dead fish in the tens to hundreds, but Sievers said it is unclear how many fish actually died because heavy rain washed away some of the fish and pollutants, and predators like raccoons may have eaten some dead fish before scientists got to the area, making it difficult for them to get an accurate count.
Any time a waterway is polluted, officials worry, Sievers said.
Residents who notice dead or struggling fish in Iowa waterways should call Iowa DNR’s 24-hour emergency response line at 515-725-8694.