RedactedNarrative: The boat was underway with 7 people on board and one being towed for skiing. They had been operating most of the day and at approximately 8:00 p.m. the boat started taking water on in the stern area. The passengers quickly pulled the skier in and everyone went to the front of the boat. Life jackets were pulled out and worn. They attempted to travel back to shore but it sank to the bottom approximately 300 feet out from shore. The passengers all jumped out of the boat in attempt to get it to float.  The boat remained under the water. It rested on bottom in approximately 3.5 to 4 feet of water and was not fully submerged but was up to the windshield area with the gunwhales just out of the water. The following day the water was bailed out and it floated once again. The owner stated he recently had a cooling hose replaced on the motor.  The hose could have been the source of the leak.  A survey of the interior of the boat did not show anything loose or not attached. I was unable to determine the exact location of the leak.