One day there is going to be a definitive underwater-swimming map - maybe a speedblast, with lots of water-filled corridors, plus the occasional little air-pocket for flags, enough megapowers to go around, and re-spawning points. However, the water here has become just a sideshow, and the main deal is a clutch of metal-lined rooms with curling staircases.
Tracer fought the "giant squid" effect, where the hapless player is caught underwater, unable to surface; it looks as if he has won, but let me know if you find differently! The screenshot is taken in the main tank, which contains a megapower and a pulsator, but is mainly for getting out of (preferably right at the top, rather than into the "room within" that you can see into here); once you are out, there are some neat places to visit, with various weapons, plus bouncers, lava pools, even a pool of water that, you can find out the hard way, is actually acid. So much metal panelwork I find gets boring, and the doors are a bit of a cheat. I suspect it's the old "can't texture movers" thing, which Tracer has cunningly worked round by makin the doors non-moving - instead, you just walk straight through them!
There is some nice stuff here, and I enjoyed helping Tracer test it, mainly by getting shot to see how a guest's re-spawning went! But it is not Tracer's most enjoyable map to date, and I am sure that some he is planning will be a lot better.