THE PLT RAISED THE HELICOPTER TO A 3 FT HOVER OVER A DOCK & WHILE TRANSITIONING TO FWD FLT OVER A LAKE, THE HELICOPTER BEGAN TO DESCENT. HE STATED THAT HE PULLED THE COLLECTIVE CONTROL & APPLIED THROTTLE TO STOP THE DESCENT BUT THE SKIDS CONTACTED THE WATER. HE THEN ROLLED THE HELICOPTER ON ITS RIGHT SIDE TO STOP THE MAIN ROTOR BLADES & BOTH OCCUPANTS EXITED THE ACFT. THE ENG WAS STARTED & FOUND TO OPERATE NORMALLY AFTER THE ACCIDENT.