It's been a while since I wrecked or lost one on the river, but here are my experiences:
1) A bad swim on Mill Creek in CA cost me a Pentax K-1000 and 2 lenses. I reported it on a renter's policy as a "flipped canoe" on a mild river trip here at home. They covered it at retail, and I upgraded to an Olympus OM2 body and 2 nice lenses. It cost me $100 deductible.
2) A 'little swim' at Deliberation on the Clark's Fork Box cost me the Olympus OM-2 and 3 lenses. I reported it on my renter's insurance policy, again, and they covered it no problem, enough so that I bought an OM4-T body and 2 nicer lenses from one of the New York discount houses. Cost me $100 deductible.
I now own a house, and haven't lost a camera on a river since that change, but have been told that if my stuff is itemized and listed, I can claim it regardless of how/where/when it is lost. I actually have found renter's policies to be far more lenient, for several different 'losses.' Just my two cents' worth, and there may be some very good 'camera specific' insurance out there nowadays. Probably a LOT more expensive, though, as the renter's policies covered all my belongings for about $175.00/year.
So many rivers, so little time..........