I have the Pentax WPi which is the predacessor to the W10 and W20. I have done some underwater photography with mine. It takes a bit of luck, and a lot of trial and error to get a good shot
I haven't tried to take any pics while fighting a fish, which would seam a bit chaotic
I have found that water clarity plays a big part in taking good pics, if there is debris in the water the autofocus may have a hard time finding the target subject. Sunny conditions work the best with underwater shots too, along with a light background too. Here are a few samples of underwater photos I've taken.
As you can see the last photo is a bit murky from suspended algae in the water. The 1st photo is super clear, because the water from that stream is extremely clear.