Farm runoff can be deadly. Seriously.

A DNR investigation in early December found that runoff from a dairy west of Bernard in Dubuque County killed over 2,000 fish in an unnamed stream in late November, the Dubuque Telegraph-Herald reports.

Casualties included minnows, shiners, chubs, suckers, dace and sunfish.

The investigation identified many factors that led surface-applied manure to run off the 40-acre field, including: heavy rains, minimal corn stock residue, field slope, inadequate separation distances, limited manure incorporation, and not checking the area for recent drainage improvements.

“This incident highlights the need for manure-application planning and for choosing low-risk areas for application,” Rick Martens, a DNR environmental specialist at the Manchester field office told the paper.