An off-duty Nassau County police officer was in the right place at the right time to make a heart-racing rescue at Wantagh Park Marina Wednesday.

"All of a sudden we heard a splash like something large fell into the water," says Officer Greg Caserta. 

An 80-year-old woman fell into the water just before 3 p.m. and was trapped underneath the dock. Caserta says there was about 20 seconds during which he and the woman's husband were desperately searching because they couldn't hear or see her.

"We didn't see anybody. We looked on the side, we looked on the back of the boat, on the dock and there was nobody," says Caserta. "My heart sank. Kinda went into panic mode at that point. "

Caserta says he eventually saw a nose and mouth and said to his father-in-law that the woman was under the dock. With his father-in-law's help, Caserta was able to save the woman.

The unidentified woman remained conscious and is expected to be OK. 

Caserta says the woman thanked him and called him a hero.