Missouri officials said bighead carp are turning up dead along the Mississippi River in counties surrounding Alton as summer heat pushes water temperatures up and oxygen levels down. The Missouri Department of Conservation said the fish are succumbing to warm water and low oxygen in shallow areas.
The die-off is hitting silver carp and bighead carp hardest, while local fish are more likely to survive the same conditions. In shallow, slow-moving pockets, the water can become unlivable quickly when river levels drop and dissolved oxygen falls.
Missouri Department of Conservation
The Missouri Department of Conservation said it is monitoring the seasonal die-off. The Missouri Department of Natural Resources said summer heat and lower river stages are concentrating fish in shallow backwaters where oxygen levels drop, which leaves introduced carp less able to withstand the stress than local fish populations.
The dead carp may resemble the aftermath of an oil spill, but officials said the cause is warm water and low oxygen. That distinction matters for anyone seeing fish in the river now: the event is tied to summer conditions, not a spill response.
U.S. Fish & Wildlife Service
The U.S. Fish & Wildlife Service said people introduced silver carp to private fish farms and water treatment facilities to control algae growth, then flooding events allowed the fish to escape into the Mississippi River. It said people introduced bighead carp for similar reasons and that those fish later escaped as well.
RiverBender said ordinary floating carp tied to this regional heat event do not need to be reported. People should report unusual pollution or distinct fish kills through the MDC Fish Kills Information page, which is the route Missouri officials want used while the die-off is being monitored.
The open question is how many dead carp have been found and whether the die-off will continue if warm, low-oxygen conditions linger in shallow backwaters.
