BUFFALO, NY — The Niagara Falls Water Board held a news conference Thursday afternoon to talk about the black wastewater discharge in the lower Niagara River last weekend.

Earlier in the day, lawmakers called for the resignation of the entire Niagara Falls Water Board.

The water board said in a statement Sunday that the discharge was due to routine maintenance of one of its wastewater sedimentation basins, however the time of work is usually done at a different time of day.

Water Board Chairman Dan O'Callaghan elaborated Thursday afternoon.

"Because of the carbon filters, the backwash is black. In this case the backwash water was treated to remove solids and contained mostly carbon fines and some suspended solids that the treatment process did not remove. This is always normal. Typically, about once a year, the Niagara Falls Water Board takes a certain quantity of water which it is allowed to do and sends it through a disinfectant process before being combined with other treated water when it is released into the lower Niagara River," said O'Callaghan.

He said the flushing has been done since 1970 with a permit from the New York State Department of Environmental Conservation.

At one point during the news conference, O'Callaghan seemed to contradict himself. First, he said the board didn't know if it was human or mechanical error that caused the large discharge of black water. Seconds later he said they are confident they know what caused the "unfortunate incident" and what needs to be done to make sure it doesn't happen again.

O'Callaghan didn't elaborate on what the problem may have been. He read from a prepared statement and didn't take questions from reporters.

The DEC is currently conducting an investigation of the Niagara Falls wastewater treatment plant, which is operated by the Water Board.