Ortlieb, the German company best known for its waterproof bicycle panniers, also makes several completely waterproof camera bags. As I said, it's completely waterproof, with sealed seams and a roll-top lid that keeps out water. Of course, from the wording in you question it may be that you actually want to USE the camera while it's protected by a watertight case. A watertight case that allows operation of the camera is a different, and very expensive, proposition. Ikelite, a long-time maker of underwater camera gear, makes the best ones.
Ikelite cases are hard, clear-plastic cases.
Another approach is taken by Ewa-Marine. Their cases are soft plastic, with an optical glass port that attaches to the lens.