RedactedNarrative: OPERATOR 1 WAS OPERATING VESSEL 1 WHILE PLOWING. AS OPERATOR 1 WAS UNDERWAY WITH VESSEL 1, VESSEL 1 IMPACTED AN UNKNOWN UNDERWATER OBJECT IN THE WATERWAY. OPERATOR 1 DID NOT SEE OR KNOW WHAT OBJECT THAT VESSEL 1 STRUCK. NONE OF THE OCCUPANTS ON VESSEL 1 SUSTAINED ANY INJURIES. VESSEL 1 SUSTAINED DAMAGE TO THE LOWER UNIT AND PROPELLER.  The operator was arrested for BUI.