Since I aspire to learn to scuba dive I'll consider myself a "diver" and answer. Actually, I carry a knife in an aquatic activity -- ocean surf kayaking -- so doesn't that qualify me to answer?
I used to have a Tekna Boot Knife -- a double-edger with small serrations near the base of the blade on each edge -- but that got lost in the surf after a big wave knocked me out of my boat.
I replaced that with a Kersaw Amphibian, which turned out to be a BIG MISTAKE. That particular Kershaw was a piece of ill-designed crap. First, it was hardly what I would have called "corrosion-resistant," having rusted badly in spots after being left in its sheath after an outing (although it had been rinsed in fresh water). The knife had a lot of grooves for grip, not to mention some small-radius serrations, which make for difficult rust removal. Add to this the fact that the skeletonized handle has an inserted rubber grip which prevented me from removing all the rust that had formed. This grip could not be removed and reinstalled. Once I lifted some of the rubber edges to attempt to remove rust that had crept under them, they would not lie flat against the metal anymore. I finally decided to use a straight-edge razor to slice off the grip entirely -- I figured I'd just have a skeleton-handle knife now. Well, what I realized -- too late -- is that the rubber grip itself is essential to the sheath's ability to hold the knife in place. A tab on the sheath fits into the hole in the rubber skeletonized grip in the handle, and that hole's diameter increases when the grip is absent, allowing too much play for the knife to remain held fast.
I replaced that sorry excuse for a design with a Benchmade H20S, made with the H-1 corrosion-resistant steel they recently released. The blade is partly serrated, modified sheepsfoot. The handle is the brightest yellow you can imagine, and really throws back light, especially at dusk, or LED light. You should see it in low light illuminated by a blue LED! The grip feels great, and the knife is lightweight, and the sheath is good. I got the knife for under $70 from Knifecenter.com
---Jeffrey