Fresh (not salt) water also helps a bit. I is most easly seen on old wood boats they fine mostley intack that are 100 years old or more.
Awhile back I read of timber that was being salvaged from the bottom of the great lakes, from way back in the days when they would harvest the timber and float it downstream. Some of the logs would be lost as they became waterlogged and sank.
The wood from those timbers is still good apparently, and it's being used to make furniture, etc...