The Mississippi River is being watched closely nearly a week after a train derailment spilled ethanol in the water. Samples are being analyzed from the site, just north of Dubuque, all the way down to Muscatine. Kevin Baskins, with the Iowa Department of Natural Resources, says 305,000 gallons have been recovered, leaving 55,000 gallons unaccounted for.

“There was a fire, so we obviously had some product that burned in the fire,” Baskins says. “There’s also some that’s still on the ice and an undetermined amount that would have soaked into the soil right there around the railroad track.” The biggest concern in this type of accident, according to Baskins, is with “low dissolved oxygen levels” in the water.

“That’s what will actually kill fish and other aquatic life,” Baskins says. “To this point, of all the samples we have, we have not really seen any low dissolved oxygen levels.” Ethanol levels in the river go from “very toxic” at the site of the spill, to “way below toxic” one mile downstream, to barely detectable 10 miles away.

Samples were even taken Monday near Muscatine, 130 miles downstream, as officials believe that’s how far the “plume” of ethanol could have traveled since the derailment last Wednesday.