Oh, poop!

The opening of the city’s first casino, at Aqueduct Race Track, has been delayed — because of massive mounds of pigeon doo-doo.

“There were pigeon droppings everywhere — on the floors, ceilings, walls, on every surface,” said one stunned official.

Genting Resorts World New York has spent more than $15 million to remove lead paint, asbestos and, yes, pigeon waste.

That’s a lot of poop — and one reason why opening day has been pushed back from spring to early fall.

The problem has triggered gallows humor that the facility should renamed “Aquaduck” or “Aquadump.”

The city Health Department calls the droppings a “small health risk” for cryptococcosis, histoplasmosis and psittacosis.

Protective clothing and even respirators are recommended for cleanup workers at the 192-acre site in South Ozone Park, Queens, which opened in 1894 and underwent its last major renovation in the 1950s.