Fish Kill Event - Des Moines River
below Red Rock Dam
- Event ID
- 1073
- Date of Kill
- 12/23/2025
- Waterbody Type
- River/Stream
- Cause Origin
- Anthropogenic
- Cause
- Gas Bubble Disease
- Mode
- N/A
- Magnitude
- 0 (Unknown/Unspecified fish killed)
- Kill Length
- not enumerated
- County
- Marion
- ESD Field Office
- FO 5
- Fisheries Office
- Boone Research Station
- LongDD
- -92.97977
- LatDD
- 41.36844
- Created Date
- 5/15/2026 8:52:06 AM
- Last Update
- 5/15/2026 9:41:18 AM
Highlighted river segments indicate those impacted in part or whole by this fish kill event. It is not meant to represent the actual extent of the kill.
Background: The United States Army Corps of Engineers (USACE) owns and operates two flood control reservoirs on the Des Moines River. Red Rock Reservoir is located in Marion County and its primary purpose is to minimize flood impacts. Red Rock Lake is located 45 miles downstream of Saylorville Lake, in Polk County.
Gas bubble trauma (GBT), occurs when fish are exposed to water that is supersaturated with gases. GBT has been linked to fish kills in the tailwaters of both USACE flood control reservoirs on the Des Moines River, but primarily below Red Rock Lake. Lutz (1995) monitored gas supersaturation-induced fish kills in the Red Rock Lake tailwaters for over a decade (1983-1994), eventually linking GBT to periods of continued high dissolved gas pressures when reservoir discharge was substantially decreased. The USACE utilized the results and altered operations in an attempt to improve conditions and fish health in the Red Rock tailwaters and downstream.
Fish Kill: An individual reported a fish kill in the Des Moines River below Red Rock Dam on Tuesday December 23rd, 2025 @12:59 PM. Staff reached out to local USACE staff to confirm the presence of dead fish in the tailwaters. USACE staff reported numerous dead fish and provided pictures.
Pictures received at 3:02 PM confirmed the presence of numerous dead fish representing multiple species. The majority of dead fish observed were Freshwater Drum. Other species observed included Gizzard Shad, Black Crappie, Bighead Carp, and Buffalo spp. Iowa DNR Fisheries staff observed gauge data for Red Rock Dam and concluded the cause of the kill was likely GBT. Iowa DNR Fisheries Staff reported the kill to Iowa DNR ESD staff at 3:16 PM. Given the history of GBT in the tailwaters and the general timing of the report and event the decision was made by Iowa DNR Fisheries staff to not conduct an onsite evaluation of the fish kill.
No additional reports were submitted by the public pertaining to this event. Following the event, data were downloaded from the Iowa DNR continuous water quality monitoring sonde located downstream of the dam. Analysis revealed that a spike in TDG% (110.36%) had occurred on 12/23/2025 (Figure 1) and was likely triggered by the rapid spike and subsequent drop in tailwater elevation.