Niagara Falls, NY - It was just a week ago when tourists and others noticed that discharge of black water into the Niagara River near the Falls. While officials of the Niagara Falls Water Board hinted previously that it may have been a mistake by a plant employee, they are now stating in a press release that it probably was the case.

With an internal investigation launched by the Niagara Falls Water Board, they have been meeting with representatives of the State Department of Environmental Conservation, which has been looking into the discharge from the wastewater treatment plant. This discharge produced the plume of black water right near the Maid of the Mist boat docks below the Falls.

The board, now guided by attorneys, has apologized for the discharge and during their press conference this past Thursday laid out two potential explanations for what may have gone wrong last Saturday.

Board of Commissioners Chairman Dan O'Callaghan said: "It is clear to us that as a result of a possible human error or possible mechanical malfunction, a large quantity of water from the sediment tank was released into the Niagara River."

Then after 9:00 on Friday evening, the board released a letter to reporters outlining the sequence of events for cleaning the tank at the wastewater treatment plant, but more specifically saying that human error was the probable cause.

The letter puts out a timeline of how the tank was being prepared for a construction project. Plant maintenance staffers tested valves on Thursday for a start to emptying the tank or basin on Friday. But it was put off till Saturday with staffing issues.

The Water Board's Chief Operator of the plant arrived early to supervise two employees, technically labeled under Civil Service status as trainees, and told them to carefully monitor the water color in a connected chlorine tank and turn off a pump when it began to darken.

After the Chief Operator left, those two workers and an Assistant Operator continued the sediment tank emptying process. Now the updated letter confirms a memo obtained Friday by Channel 2. It notes that the one employee who was assigned to monitor the outflow and water was called away by another worker to to another part of the plant to assist with another task. And when he returned, he noticed the darker colored water and reported it to the Assistant Operator. The pump was then turned off.

The board says: "it is our preliminary belief that the pump in the tank or basin was allowed to run longer than intended, which caused a higher concentration of the backwash water into the chlorine tank than occurs under normal conditions."

The Board Chairman on Thursday would not answer specific questions from Channel 2's Dave McKinley and other reporters, only saying it's under investigation. McKinley asked: "How much of this was human error?"

Contacted Saturday, a DEC spokesman in Albany would only say it's an ongoing investigation. That is even after that probe was formally announced in a press release by Governor Cuomo days after the incident. Politicians at every level have been calling for more inquiries and even hearings.

Despite saying they were not exactly sure of the cause, the Board Chairman then turned around and

said on Thursday: "We have been in discussion with the DEC about the details of what occurred, and we are continuing these discussions for the coming days. We are confident that we have identified the cause of this unfortunate incident and know that we...what needs to be done to make it not happen again."

A call for clarification to the Niagara Falls Water Board Executive Director Rolfe Porter was also not returned on Saturday.