KEOKUK — An overflow at the Roquette America plant in Keokuk sent about 40,000 gallons of process wastewater into the Mississippi River Saturday morning.

The tank overflowed about 1:30 a.m. Plant officials are not sure what caused the overflow, speculating that a slug of process wastewater may have caused the problem. Plant workers reset the breakers and restarted the pumps, ending the overflow in about 15 minutes.

Large amounts of wastewater can deplete oxygen in the water needed by fish and other aquatic life.

The DNR did not require Roquette America to take or test water samples because the discharge lasted such a short time. Given the volume and speed of the river, the wastewater would have been down river before staff could collect samples.

Roquette manufactures cornstarches, corn syrup and other products using a corn wet milling process.