RedactedNarrative: VESSEL 1 WAS REPORTEDLY TRAVELING NB ON LAKE POYGAN At 12 MPH.  VESSEL 1 OBSERVED A BUOY (RED P-10) AT THE LAST MOMENT AND STEERED LEFT TO AVOID COLLIDING WITH THE BUOY.  THE OPERATOR OF VESSEL 1 SAID THAT THE BUOY WAS UNLIT.   THE OPERATOR OF VESSEL 1 SAID THAT HE BELIEVED THAT HIS PROPELLOR MAY HAVE STRUCK THE CHAIN OR CABLE THAT HOLDS THE BUOY IN POSITION.  VESSEL 1 OPERATOR SAID THAT HIS ENGINE CONTINUED TO RUN POST-COLLISION, HOWEVER HE SAID THAT HE HAD NO PROPULSION.  VESSEL 1 THEN BEGAN TO TAKE ON WATER THROUGH THE ENGINE COMPARTMENT UNTIL IT SANK.  THE OPERATOR AND PASSENGER RECEIVED A RIDE HOME FROM A SECOND VESSEL.  CONTACT WAS MADE WITH VESSEL OPERATOR APPROX 8-9 HRS AFTER THE INCIDENT REPORTEDLY OCCURRED. INVESTIGATION FOUND THAT THE BUOY VESSEL 1 REPORTEDLY NEARLY STRUCK HAD AN OPERATIONAL FLASHING LIGHT ON TOP.