RedactedNarrative: Vessel 1 (V1), operated was leaving the area of Conrad Island, on the Occoquan River, Fairfax, VA. Vessel was returning to the boat ramp at Occoquan Regional Park. The vessel was occupied by seven adults. Operator observed the vessel taking on water. He did not hear or feel a collision of any kind. He observed the bilge pump was ineffective. The vessel came to rest on the river bottom half submerged on a shallow sandbar between Conrad Island and the start of the no wake zone (38°38.917' N, 077°13.401' W). This was approximately twenty yards outside the channel. It was low tide. A second vessel associated with the first made several trips to ferry everyone to safety. The salvage crew observed a broken water line. It is likely this maintenance failure cause water to be pumped into the vessel, overwhelming the bilge pump resulting in a sinking. No one was injured. No pollutants entered the waterway. The vessel was recovered at 1400 the following day.