The cloudy black water beneath Niagara Falls came back Monday morning.
Discolored water could be seen below the world-famous cataracts, a scene similar to what became an international spectacle over the summer.
The Niagara Falls Water Board said in a statement that the discharge resulted because of "heavy and prolonged rainfall" that caused the treatment system's storage and processing areas to exceed capacity.
The Water Board said its treatment system "lacks substantial storage facilities, so when flows exceed the plant's treatment capacity due to heavy rain, a discharge or overflow cannot be avoided."
Reports from the scene near the Maid of the Mist docks at around 11 a.m. indicated a strong odor of chlorine in the area.
Wet weather often causes overflows of sewage and rainfall from municipal sewage systems when their capacity to treat sewage and stormwater is exceeded. Niagara Falls' treatment system, like those of many municipalities in the state, combines stormwater runoff and "sanitary sewage" from toilets and sinks.
Sewage system overflows are typically not black in color. The Water Board said in its statement it has no control over the color or turbidity of discharges during a "wet weather event."
More than 1.2 inches of rain had fallen at the Niagara Falls International Airport as of about 8 a.m. Monday, according to the National Weather Service.
The first time the black discharge flowed into the Niagara River was July 29, an incident that gained international attention. There were three unplanned discharges from Niagara Falls' sewer treatment system last Wednesday, also triggered by rainy weather.
Last month, the state Department of Environmental Conservation fined the Niagara Falls Water Board $50,000 for a series of discharges, including the one from July 29.
Niagara Falls' treatment plant can treat about 60 million gallons per day, according to the Water Board. The plant utilizes a treatment process that is both chemical and physical – part of the process involves filtration through carbon.
Most modern wastewater plants use a "biological" treatment process, the Water Board said.
The Water Board "is examining long-term solutions to these issues, including converting its wastewater treatment plant to biological technology, and constructing additional storage capacity to reduce untreated or partially treated wastewater overflows," the agency said in its statement.
The rain across Western New York on Sunday and into Monday triggered overflows in waterways throughout the area. The NY-Alert notification system reported 13 sewage overflows in Erie County on Monday as of about 10:30 a.m. The only reported discharge in Niagara County as of 12:45 p.m. was in the Niagara River in North Tonawanda. There, an estimated 3 million gallons had been discharged on an ongoing basis over a 24-hour period.
As of 1 p.m. Monday, the NY-Alert notification system had not issued any information about the discharge below the falls.
The Water Board said Monday's discharge was reported immediately to the DEC, as the state agency has instructed.
The DEC said Monday it is investigating the latest discharge near the falls.
In a statement late Monday afternoon, the DEC said it is "responding to a report from the Niagara Falls Water Board of overflows and discharges associated with the Niagara Falls Wastewater Treatment Plant and sewage system. While the discharge occurred at a time of heavy rain in the area, DEC’s investigation is ongoing at this time. DEC will provide additional information as it becomes available."