I've been caching since 2004 and have run into this a lot. If you find a cache that was placed in a poor location that eventually ended up in water. You can tie a tether to it or move it slightly to secure it. I've yet to encounter another cache owner who wasn't appreciative of this gesture. Make sure you log on the cache listing that the cache need maintenance. I would definitely try to secure the container some how. Wet logs are far too common, the only thing you can do is replace it with a new baggy and fresh log sheet. I carry several in my pack along with other materials to help out other cachers.