Hello, and Welcome to MyGMRS Forums. The bubble pack radio range and distance claims are published under "laboratory conditions" from one wilderness mountain top to another. In real world scenarios, you can probably expect an effective range between identical radios, under average terrain situations, of 2 to 5 miles max... and in most cases quite a bit less. As Logan5 mentioned, a cell phone in a specifically designed waterproof bag is your best bet. The only way that I would rely on GMRS ONLY is to set up a temporary base station and gain type antenna at a staging area midway between your river entry and exit points and TEST the radio reception from shore all along that route BEFORE your departure and have someone stationed at that temporary base station during the trip. You also may wish to verify that there actually IS cellphone service in those areas as well - before you venture out. Rarely are any specific GMRS frequenices monitored routinely by official agencies for emergencies. That type of network simply does not exist. Best of luck and be safe...