A firefighter saved a drowning man from the frigid East River near Gracie Mansion yesterday, authorities said.

The man, whose name wasn’t immediately released, went into the 40-degree waters near 86th Street at about 6 p.m. when his rubber raft deflated.

Two cops summoned help, and a 65-foot FDNY craft sped upriver from the Brooklyn Navy Yard carrying firefighter Michael Krochak, who jumped in to rescue the freezing boater.

“His teeth were chattering and his skin was red,” Krochak said. “He’s a very lucky kid.”