The company might be subject to large fines and restitution fees for the dead fish.
The effects of the river contamination continued into Missouri, where the Nishnabotna flows about another 10 miles until it reaches the Missouri River. Lorenzen said conservation officials in that state discovered dead fish near the mouth of the river.
In smaller concentrations, the fertilizer contamination can result in a lack of oxygen that kills fish, Lorenzen said.
“However, this was such a large amount of chemical, it more than likely killed the fish from acute toxicity … killing cells at the gills.”
Lab tests to determine the severity of the contamination were still pending on Friday.
The lasting impact on the fish populations is not yet clear. Lorenzen said many of the game fish such as catfish and walleye are likely still in the Missouri River, where they stay during colder months until returning to the Nishnabotna rivers in the spring.
Large numbers of small fish — which the bigger fish feed upon — have died, but those populations can be restored by fish that survived upstream from the spill or in the numerous tributaries that were not affected by it.
It’s possible that the fertilizer killed turtles, too, that buried themselves in sediment of the river bottom for winter. Lorenzen plans to return to the area in late spring to see whether turtle carcasses have floated to the river surface.
The DNR recommends that residents with water wells near the river have their drinking water tested for nitrate, a service that is free through county environmental health departments.
