Gov. Andrew Cuomo on Tuesday cast doubt on a city agency’s claims surrounding a foul-smelling discharge that turned the water near the base of Niagara Falls black at the height of a busy tourist weekend.

A day after directing state regulators to investigate, Cuomo, a Democrat, raised the possibility of criminal action “because that situation could have been potentially serious.”

Black water spewed from a pipe along the American shoreline and crept well into the Niagara River on Saturday afternoon, alarming residents and tourists who complained about the sight and smell. The inky water enveloped the dock for the popular Maid of the Mist tour boats.

The water board for the city of Niagara Falls said it had emptied a sediment settling basin at its wastewater treatment plant during the course of routine maintenance. The basin is used for backwash water from cleaning the operation’s carbon filters and does not receive raw sewage, the governor’s office said.

The water board said the discharge contained accumulated solids and carbon residue “within permitted limits.”

Cuomo disputed that claim after an event in Hudson on Tuesday.

“The original version of — ‘Well, we did this and this was pursuant to a (Department of Environmental Conservation) permit’ — I don’t believe is true,” Cuomo said. “They have a DEC permit to operate the facility, but it has to be operated in a proper way.”

Releasing carbon filter backwash into the river is permissible, state officials said, but only if it doesn’t otherwise violate state water quality standards. Those standards prohibit discharges that change the odor or appearance of the Niagara River.

The DEC said it was unlikely the discharge posed a threat to human health or the environment because water coming over the falls would quickly oxygenate it. There were no immediate reports of fish kills, and the plume had dissipated by Sunday morning.

Niagara Falls Water Board Executive Director Rolfe Porter did not respond to telephone or emailed messages Monday and Tuesday seeking information about previous discharges.

(AP)