RedactedNarrative: Vessel was underway, near James Bay on Lake Mead and a fire started in the engine compartment.  Vessel fire extinguishing system automatically activated.  Vessel operator also manually activated the engine compartment fire extinguishing system from the helm.  The operator was unable to open engine compartment hatch because of the fire damaged electrical system.  Vessel owner/operator estimated the damage at $75,000.  Vessel was towed to Las Vegas Boat Harbor.