I agree with Mr. Gillespie. The condition of an aircraft in the water depends on the type of water (saltwater and fresh) and the depth. The depth seems to control the growth of organisms on the structure.
When I worked at the San Diego Aerospace Museum, our team was restoring an F4F Wildcat. The Wildcat had been recovered from Lake Michigan, where it had crashed during pilot training in 1942. We were working on it 56 years later. Some of it was in bad condition (as a result of the recovery and other attempts from amateurs to recover it) and some of it was in surprisingly good condition. Obviously, it had been sitting in cold fresh water, instead of salt.
The areas on the Wildcat that had the least amount of corrosion and damage were areas that had liberal application of zinc chromate primer, or were protected with cellophane tape during its original construction. Places where two different metals met were the most corroded, except where some assembly line worker had lovingly applied cellophane tape. I remember one assembly shown to me by a fellow who had worked for Grumman during the war. "See that," he said, showing me cellophane tape over an assembly that had very little corrosion. "Somebody built this thing knowing that someone's son or husband would be flying it. They knew the pilot's survival may depend on the durability of what they were constructing. No one builds stuff like this anymore."
It brought tears to my eyes.