NYC Parks says the Red Hook Pool closed on Sunday due to unsanitary conditions in the water.

Dozens of Brooklyn residents walked in the double doors, only to walk right out on Monday because they say they were unaware of the closure.

"I'm really upset that the pool is closed, it’s a hot day<" said Pearl Bowie-Harmon, of Prospect Lefferts Gardens. "I [came] all the way over here from Prospect Leffert Gardens so I could do a back float, and it’s closed! I’m debating on whether I should go another pool or just call it a day and go tomorrow indoors.”

NYC Parks says as per regulation, it takes about 25 hours for the water to sanitize before it's safe for swimmers.

Parks says the pool will re-open on Tuesday at 11 a.m.