Yeah, I know how that goes....
1) Protect the camera gear. At least double bag it. Every piece of gear could be in a heavy duty zip lock with some foam rubber. If the pack happens to go swimming, it may bounce some rocks.
2) Put the zip locks in a dry bag. Blow it up and seal it.
3) Same for your pack liner. DO NOT compress your pack. If it goes swimming, you want it as a life preserver, and, you do not want to let it loose.
4) Felt pads (usually these can be purchased from a good fishing shop as replacements) can be
rigged around your shoes with a couple holes. These provide excellent traction on slick rocks, but fail on gravely bottoms.
5) You really should carry a hiking staff rigged with a 1/4" screw on top as a camera mount.
The staff will act as a third leg while wading, and acts as a fair substitute for a tripod.
If you have extra film (what??? FILM????), also, double bag that. Humidity can raise heck with it, depending on which type it is. Difficult to clean off if it gets damp or wet.
I usually bring a 80-300 zoom and a 20-70(maybe it was an 18-60??) macro/zoom. There is a small range that isn't covered, of course. There is also a 2x extender...it can be difficult to use but better, weight-wise, than bringing a larger lens. You have to use manual settings, though... no point and shoot, though exposures are usually OK...
Again, all wrapped in foam, duct tape wrapped. Makes the lightest carrying cases I know of. The closed cell foams are the best, since, they do not absorb water...you knew that.
Anyway, if I am out to take pics, thats what I do. I actually got wet once and my gear stayed very dry, so, I know this works...though, it adds about 10# to my pack.