I thought maybe ice would act as a preservative, I guess.
This is regards to salt water, I am not sure if fresh water is different.
****Forensic explanation alert-weak stomachs scroll on by***
http://www.scientificamerican.com/blog/post.cfm?id=how-long-do-dead-bodies-remain-inta-2009-06-10
"A 2002 study in the journal Legal Medicine examined nine bodies that had drifted hundreds of kilometers in cold waters off the coast of Portugal and Spain. Bodies recovered in the first week were in good condition, but the beginning signs of decomposition were present on a body recovered after eight days. The two bodies recovered after 20 days were highly decomposed and could only be identified through DNA analysis or dental records. As for warmer water, A 2008 study on two human bodies recovered following aircraft accidents found one body off of Sicily to be partially skeletonized after 34 days and a second body off of Namibia to be completely skeletonized after three months.*"