Thousands of trout, chubs, suckers and dace mysteriously died in a small section of the Whitewater River over the summer.
After months of investigation, officials still aren't totally sure why.
The DNR said Tuesday the probe was "unable to pinpoint a cause" for the fish kill. About 9,000-10,000 were found in the river, in a section northeast of Rochester on July 30 – a couple days after heavy rain.
Their best guess: A "combination of biological, chemical, and environmental conditions" stemming from the 1-2.5 inches of rain that fell into the Whitewater River over the course of just a few hours.
"In such situations, fish may die quickly and there is often little or no accumulation of toxic compounds in their organs and tissue," the DNR wrote.
Investigators from three state agencies analyzed tissue form dead fish, took water and soil samples, and performed other tests in the weeks following the kill. Officials also interviewed nearby farmers, landowners and pesticide applicators.
They found almost nothing: No toxic levels of ammonia, pesticides or metals in the water samples; no insecticides, and only "extremely low" levels of fungicides; no evidence of illegal dumping, unusual wastewater discharge, or "inappropriate" use of manure.
However, in situations like the sudden burst of heavy rainfall experienced two days earlier, "fish may die quickly and there is often little or no accumulation of toxic compounds in their organs and tissue."
The DNR though notes fish kills are "not uncommon," and this July incident did not kill all the fish in the river – the populations should bounce back with some restocking, according to the agency.
You can read the full report – which is 367 pages long – by clicking here.