Ontario has sewage overflows that spill into the Niagara River too, says the chair of a water board in Niagara Falls, N.Y., adding that they're almost as bad as the American leaks, just less visible to tourists.

Daniel O'Callaghan, chair of the Niagara Falls Water Board, penned a letter to NDP MPP Wayne Gates this week outlining just that. The letter came after Gates wrote an open letter saying a recent American dump of raw sewage hurt the environment and the economy.

O'Callaghan said that he appreciates the concern — but Niagara Falls, Ont. overflows are nearly as bad as the ones from Niagara Falls, N.Y.

O'Callaghan wrote that in 2017, the Ontario side discharged more than 834 million litres of raw or partially treated sewage into the Niagara River. The American side discharged 945 million litres. The difference is that fewer people noticed it.

"The Canadian discharges are less visible than those of the Water Board because of the locations where they enter the Niagara River," O'Callaghan wrote on Aug. 31.

So "we look forward to seeing you become more active in addressing this issue in the territory that you represent."

The Maid of the Mist is shown travelling through black-coloured wastewater treatment discharge in the Niagara River near the American side on Saturday, July 29. (Patrick J. Proctor/Rainbow Air Inc./AP)

Discharges into the Niagara River made headlines earlier this week. That's when a water treatment facility in New York state released more than 30 million litres of wastewater and stormwater into the river.

The overflows are an ongoing saga that came to a head in July 2017 when an inky, foul-smelling discharge blackened the water near the base of Niagara Falls during a busy tourist weekend.

Gates wrote a letter to Ontario's environment minister Wednesday about the latest discharge. He called the situation "nothing short of an environmental catastrophe."

"This issue has been going on for far too long and continues to threaten the health of our beloved Niagara River," Gates wrote.

"I am asking you to reach out to your federal counterpart and counterparts in Niagara Falls, N.Y., and find a way to ensure this never happens again."

O'Callaghan said the water board is working hard to reduce sewer overflows.

"We share your concern regarding the water quality in the Niagara River," he wrote to Gates, but added that Canada has work to do too.

"The hardworking employees of the Niagara Falls Water Board, various New York State officials, and many others have already been tackling this issue of improved water quality in the Niagara River for quite some time."