I think this is the best answer. Wildlife photography can be as gentle and easy-going, or as thrilling and danger-fraught, as the photographer wants it to be, and as far as I can tell it still remains ‘socially acceptable’.
No it isn’t. That is true for a small number of trout streams, but it isn’t the norm. It’s just plain untrue for walleye, northern pike, largemouth or smallmouth bass, bream, crappie, etc.
I’m not talking about that either, perhaps you are unaware that many sports fishing streams US are stocked with farm raised fish placed (dumped) in the streams for people to catch.
OK perhaps I am most familiar with trout which it is very common around here, even having guys follow the DEC truck to see where they dump them with rod and real ready to go.
Is there a problem with the occasional fish getting hurt with a catch and release fisherman? Hell, I eat fish that I didn’t even catch. There are even fish, like those Asian snakehead fish that have ended up here in many of the US fresh water rivers, lakes, etc., that need to be put into extinction. I fail to see a problem that needs to be solved here.
Yeah, birdwatching came immediately to mind. Inexpensive, nice camaraderie with other like-minded people, great internet resource and social exchange, and best of all, travel as much as you want with all the backcountry wandering and adventure, and never need to buy a non-resident license.
I’ve done this, in England. Good fun, and often yields an impressive catch. As for equivalents of conventional angling both satisfying to the angler and suffering-free for the fish – no ideas which haven’t been suggested by other posters, I’m afraid.
Learn mushroom hunting. With minimal instruction it’s much, much safer than most imagine. It satisfies the hunter-gatherer urge and gets you out of the house and interacting with nature.
Composing music inspired by the water (a la Handel).
Writing essays, poetry, etcetera inspired by the idyllic setting (a la Thoreau).
—G!
Catch and release is, according to Alaska Native culture, playing with your food and disrespectful to the animal. I agree.
I took up both woodworking and guitar to amuse myself. If I want to go out into nature, I either sit and read, or I hike and take pictures.
Canoeing, climbing, hiking, swimming, sailing, bicycling, bird watching, gardening, outdoor painting, paintballing, skateboarding, etc.
There’s no real shortage of outdoor activities that one can engage in, near or away from water.
Learn how to make all wood bows and arrows. Very addictive once you get started so approach with caution. You can apply science, history, nature, physics, art all at the same time.
Noodling.
Or, photo safari to find Bigfoot.
Neither hobby harms the catfish (your arm may get chewed on) or the Giganthropithicus.
Don’t use a barbed hook.
How about photography?
Get a motorcycle.
Marine life conservation work.
If you’re near the sea, you could go crabbing - no hook - just a bunch of old bacon rinds or other suitable bait tied to a piece of string and a weight - lower it into water near piers, etc and pull it up after a minute or two - the crabs are generally too stupid to let go until you’ve got them over the bucket. Release the crabs at the end of the session.
It’s normally considered an activity for kids where I live, but that doesn’t stop me.
The underwater camera thing sounds interesting. I’m planning a project like that myself (although just with an endoscope camera on a long pole).
I’m a fisherman who’s gotten interested in the underwater photography thing. I’ve been using one of these on my boat, but find it hard to see fish. I’ve recently gotten interested in searching for remains of submerged towns. Most of the lakes in Texas are man-made, and many have covered over whole towns. I found some sort of remains near the old site of Preston, but so far my finds are merely some oddly geometric returns on my boat’s sonar. I’m experimenting with a submersible “light-box” to send down with the camera, since the little infrared lights on it don’t illuminate very far. My first attempts at building it are working OK, with no leaks after 30 minutes at 40 feet. I’m gradually increasing times and depths.
I’ll report back if I find and/or film anything interesting. My search for the alleged “giant catfish” along the deep part of dams has been fruitless. 
I rarely fish when I kayak. Sometimes I carry binoculars and do some birding. Sometimes I bring a camera and take pictures. Usually I bring a few beers and a joint. Cleaning up waterways is another on-the-water activity I do from kayak. When I paddle a local lake frequented by Amish guys I collect found bobbers/lures/etc and give my finds to Amish fishermen who are fishing for sustenance.
Professional, full-contact picnicking.