Cops and firefighters rescued three men from the East River yesterday after their boat capsized while they were setting up buoys for a canoe regatta.

The men had been preparing for the Liberty Challenge, a 15-mile regatta, when their motorboat flipped over just before 8 a.m. after one of its lines got caught on a cleat.

Police Lt. John Rogers and Detective Darin Caputo, as well as Steven Hoek, an FDNY swimmer from Marine 3, rescued the men.