The collision Monday involved four barges loaded with gasoline and another barge carrying cumene, a toxic chemical used in making plastics.
One barge leaked an estimated 69,000 gallons of gasoline into the river, Coast Guard spokeswoman Angel Deimler said.
However, Deimler said sunlight had dissipated much of the gasoline, and the remainder, mostly a floating sheen, had not drifted far.
"The wind was working with us and kept it from spreading," she said. "It's stayed within a two-mile area. Mother Nature was on our side."
Coast Guard Ensign Kevin Floyd told The Courier-Journal of Louisville, Ky., that another of the gasoline barges and the cumene-laden tanker also were leaking. Cumene can irritate eyes and skin and cause respiratory problems.
No injuries had been reported.
Foam was to be brought in to soak up any remaining gasoline, said Tim Fleming, assistant fire chief of Mount Vernon Fire and Rescue.
Officials hoped the river and intake valves downstream could be reopened by Tuesday night.
Mount Vernon, a city of about 7,000 that relies on Ohio River water, closed its intake valves 45 minutes after the accident and hauled water from Morris Township.
"We're waiting for it to pass," said Wanda Bennett, an employee at the Mount Vernon Water Works. "We are operating on our reserves."
In Kentucky, the town of Morganfield closed its river intake and relied on a nearby reservoir, water plant manager John Coffman said.