Iowa DNR
Iowa DNR Fish Kill Database

Fish Kill Event - Winnebago River

starting B20 bridge on north side of Mason City

Event ID
Date of Kill
Waterbody Type
Cause Origin
1 (1 - 100 fish killed)
Kill Length
8.00 miles
Cerro Gordo
ESD Field Office
FO 2
Fisheries Office
Clear Lake Station
Created Date
3/26/2019 12:07:42 PM
Last Update
3/26/2019 12:07:42 PM
For more information about this fish kill event, contact the Field Office or Fisheries Office listed above.
Impacted Assessment Segments
Lat/Long uses WGS84 datum
Onsite Comments

The carp were in various stages of decomposition indicating the mortality event had occurred over 3 or 4 days. Some remains were nearly intact while others were nearly skeletal.

The fish kill consisted of large carp, only. No other species of fish were found as part of the fish kill. One to several dead carp was noted at various locations along the Winnebago River between the B-20 Bridge (i.e. upstream) and the Highway 18 overpass (downstream). The upstream location is in the north part of Mason City (Section 33, Lime Creek Township). The downstream location is southeast of Portland (Section 20, Portland Township). The stream distance is estimated at 8 miles. Live minnows and live carp were observed within the fish kill portion of the Winnebago River. I believe the fish kill was due to natural causes such as stress and/or disease. The last downstream area checked was the bridge at the Clay Banks Recreation Area which is about 3-4 miles below the Highway 18 overpass. No mortalities were found. More than a dozen live carp were observed in a small shallow water area.