Carp are turning up dead in stretches of the Mississippi River near Alton, and wildlife officials say the fish are losing to harsh summer conditions in shallow water. The die-off is being driven by warm water and low oxygen, with silver carp and bighead carp hit the hardest.
The Missouri Department of Conservation said the fish are showing up dead in counties surrounding Alton, while other reports have come from several Mississippi River locations. The agency said summer heat raises water temperatures and lower river levels leave less dissolved oxygen for fish to breathe, which can make slow-moving pockets quickly unlivable.
That pattern matters because the same warm, shallow water that is taking a toll on invasive carp is part of the broader summer environment that local fish are more likely to survive. Officials said introduced carp are less able to withstand those conditions than native fish populations, and the Missouri Department of Natural Resources said fish are being concentrated in shallow backwaters where oxygen levels drop even further.
The species being hit also helps explain why the die-off is drawing attention. The U.S. Fish & Wildlife Service says silver carp and bighead carp were brought in for human uses and later escaped into the Mississippi River, where they spread through flooding events and became a long-running problem for the river system. Missouri officials are treating the current mortality as seasonal, not as a sign that every carp found floating should be reported.
The Missouri Department of Conservation said it is monitoring the event with partner environmental groups, and people are being told to report unusual pollution or distinct fish kills through the MDC Fish Kills Information page. Ordinary floating carp tied to the regional heat event do not need to be reported, but a separate pollution problem or an unusual cluster of dead fish would still merit a call. For now, the unanswered question is how widespread the die-off has become across the river, because officials have not said how many carp have died.
