Tens of thousands of gallons of nasty, only partially treated sewage was accidentally unloaded into a Long Island bay for roughly 15 straight minutes on Sunday, state officials confirmed. 

Nearly 30,000 gallons of sewage water that had not been disinfected was dumped into Reynold’s Channel in Long Beach — forming a nasty-looking, dark-colored sludge — after a plant operator failed to close a valve, according to Long Beach officials. 

That failure, according to state and local officials, caused an overflow into the facility’s stormwater system that sent the waste pouring into the waterway near the city’s fishing pier.

For 15 straight minutes before anybody noticed, that sludge overflowed from the plant’s primary digester tank and spread onto surrounding surfaces before finally reaching the stormwater system that drains directly into Reynolds Channel, officials said. 

A multi-day clean-up was undertaken by Long Beach city officials, which is now complete in the waterway as they work to clean up the storm drain system, according to state officials.

The State Department of Environmental Conservation is now investigating the incident and monitoring the conditions for public health safety, an agency spokesperson told The Post. 

There are no known, immediate impacts to any wildlife or marine life, state officials said, although it is unclear if the waterway is safe to return for fishing or swimming activities. 

In April, researchers from Stony Brook University discovered that a potentially deadly, flesh-eating bacteria — vibrio vulnificus — was living inside multiple Long Island waterways.

The bacteria is partly caused by nitrogen runoff from similar sewage water, mainly from septic tanks that leech the waste into the region’s waterways.

Reynold’s channel was not one of the bodies of water found to have the bacteria living within it.