More than 40,000 gallons of crude oil gushed from the Exxon Mobil pipe below the riverbed.
As cleanup continues, teams of federal and Exxon Mobile workers are trying to gauge the damage and see if any animals were hurt.
Exxon Mobil Pipeline Co. president Gary Pruessing said the damage is limited to a 10-mile stretch of river.
But Gov. Brian Schweitzer dismissed Pruessing's claim as premature. The governor said Exxon Mobil needed to get more personnel to inspect the situation close-up. He also slammed Pruessing's statement to reporters that no injured wildlife had been found.
"For somebody to say at this early stage that there's no damage to wildlife, that's pretty silly," Schweitzer said. "The Yellowstone River is important to us. We've got to have a physical inspection of that river in small boats - and soon."
Local media have carried photos of apparently oiled pelicans and turtles. The Environmental Protection Agency said it can't confirm any damage to wildlife or fish kills, but investigators were checking and the federal agency expected to know more Monday.
The Associated Press contributed to this report.