New York Gov. Andrew Cuomo has directed state regulators to investigate wastewater discharges that turned the water near the base of Niagara Falls black last weekend.

The Democrat announced Monday that the City of Niagara Falls may have violated state water quality standards Saturday when the local wastewater treatment plant discharged foul-smelling, black-coloured water into the Niagara River just below the falls.

Violations of the state's water quality standards are a serious issue, I have directed DEC to immediately get to the bottom of this event. —@NYGovCuomo

The dark water enveloped the dock for the popular Maid of the Mist tour boats on the U.S. side of the falls.

Officials with the city's water board said the discharge was part of routine maintenance of one of its basins. The murky water had dissipated by Sunday morning.

Neither the mayor's office nor the water board returned telephone messages to the AP on Tuesday.

Cuomo says the Department of Environmental Conservation is conducting the investigation. Violations carry a maximum penalty of $37,500 US each.