In my setting, some humans hundreds of years ago became aquatic due to magic (the same setting has vampires pretty much like in the original Dracula novel, who descend from one guy who became a vampire due to same magic).
What should the aquatic humanoids look like in order to be believable? They live in lakes up to at least 425 meters deep (possibly up to 1642 meters which is the depth of Earth's deepest lake, i haven't decided), across Europe and possibly continental Asia. Maybe they'd also be somehow viable in salt water?
I thought they'd have webbed fingers and toes and can't breathe air, but beyond that i'm not sure. Even though their ancestors became like that due to magic, i still want their appearance and abilities to make environmental sense. Coloring, fins, etc. They're ultimately still humans, enough to reproduce together and produce propably infertile hybrids, so they can't be too alien. They'd propably still be omnivorous humanoids too.
Would they also propably need to have superhuman strenght/toughness in order to be able to survive and casually move under all that pressure, and generally be able to tread water constantly?
Also, ideas on explaining how they've spread across the mostly unconnected water bodies despite being unable to survive on land?