Aliens who live in fresh water. Obligated by treaty to eat zebra mussels. There do not appear to be any saltwater versions, and they have different responses to brackish water.
They look human, but exhibit superstrength, enhanced vision, immunity to pressure, and the ability to breathe water (gill slits become evident in water). Some of them seem to be bullet proof; some are not. Given the medium they live in, they tend not to use projectile weapons.
There is a nice trade with them in dealing with waterproof items. However, they’re not a large market. The current estimate is that there are six city-states throughout the Great Lakes, comprising between one hundred and fifty thousand and two hundred thousand individuals.
Variation seems to be important: they have wildly different views on interaction with humans, technology, magic, and so forth. Some of their young come to dry land because they like the technology: those tend not to be psionically gifted. The variation is extreme: some of them are essentially obligate water-breathers, others only need to breathe water once a day for half an hour, and everything in between. Kevin Atlantis, a student at St. Clair University in Steel City, only needs to breathe water for an hour a day; his father needs to breathe every two hours, and his mother in between.
These estimates might be wrong.
Technology exists to create human-Atlantean hybrids. What we call psionics or magic, they call technology but won’t explain it to us. Security, don’t you know. Some fraction of Atlanteans are psionic, and so far more females than males have been seen to be psionic, but that’s not absolute.
They are not common in Steel City; the effluent from the city tends to be not of the cleanest, and the area is taboo for other reasons.
The effluent in the river is in violation of their treaty with us, but for various reasons (because the area is taboo?) this has not been pressed. The recent ascension of !Mok’kar to the throne of Lemaris (the nearest city) seems to have changed this situation, and !Mok’kar has send a monster to punish the humans.
Names tend to be clicks, glottal stops, and whistles (given as (rising)(falling)(level), though really it should distinguish between the six whistle tones. Clicks are indicated in writing as !, glottal stops as ?, and uvular expressions as ’.