I've been working on the master angler achievement for a while, about 3/4 done.
My thoughts are that you should be able to clean fish at a provisioning station and do so faster than in the wild. Maybe even in lots of 10 like refining.
Maybe a craftable bait that increases the chances of catching blue and green fish but reduces the chance of catching furnishing fish. Maybe it would require perfect roe to make to balance the risk/reward aspect.
As for swimming, how about "sprinting" to swim faster. Still uses stamina, just makes swimming less tedious.
Perhaps a Fording skill added to the riding training at the stables. That way people can swim if they want to, or stay mounted and let the mount swim. Nothing worse than going cross country and hitting a river with a small deep spot and getting dismounted only to swim for 5-10 feet and stand up. Obviously you would still take damage in Cyrodiil due to the slaughterfish and the deepwater boundry areas in the rest of the game.
Maybe even special boat "mounts" that can be summoned while swimming. Like a log, raft, canoe/kayak. nothing big or fancy, just something to make water crossing easier.