An undetermined amount of manure escaped from Black Soil Dairy — which has about 4,500 dairy cows about three miles south of Granville — before the dairy owner noticed and stopped the leak Monday morning.

The dairy farm has a flush flume system to clean manure from its three barns. It works by cascading a shallow stream of fast-moving water to wash manure from barn floors. Part of the system in one of the barns became clogged by sand that is used for bedding last week and caused the overflow.

There was no easy way to quantify the amount of manure that had leaked because it didn’t spill from a storage container with a known capacity, said Jennifer Christian, a senior environmental specialist for the DNR.

“It was a significant spill, which caused a fish kill,” Christian said.

On Tuesday, DNR investigators noticed the manure had gone five miles downstream of the dairy farm in Deep Creek, which is populated by small fish such as chubs and minnows. The full extent of the environmental impact of the leak was unclear because ice covered parts of the creek, Christian said.

It’s possible the dairy farm’s owner, Nate Zuiderveen, will attempt to pump contaminated water from the creek, Christian said.