RedactedNarrative: Vessel 1 was towing a tube with two children on it.  Operator of vessel 1 stated he was aware of a swimmer in the water prior to the accident.  Upon returning to the dock , towing the 2 children on the tube, the operator of vessel 1 struck the swimmer in the water approximately 100 feet from the dock while traveling approximately 10 miles per hour.  The female swimmer who had been struck was taken to the hospital with multiple injuries and spent several days in intensive care.  Investigation revealed; operator of vessel 1 failed to keep a proper lookout and was traveling at a speed greater than 5 miles per hour approaching a dock.