Anthro-Alligator Snapping Turtle? That's beautiful
Thanks! I came up with them when someone was complaining about Halflings as "riverfolk."
Mechanically, I kind of melded Lizardmen with Dwarves. In terms of fluff, they were gruff but stalwart (like Dwarves) but fought with extreme rage (Orcish traits). Like Vikings and the Halflings that inspired them, they spent the bulk of their lives on the water and were formidable traders.
Things I've done with other races:
Elves:
In one campaign, they were hermaphroditic Grays whose scientific survey ship had crash landed on a world where magic worked, and the crash itself resulted in the ship being buried. (S3 Barrier Peaks, anyone?) Their tech was advanced enough for them to generate a huge slow-time/stasis field which let them wait for rescue. They had devices to help them somewhat resemble the other sentient races of the world. Thus, common legendary tropes about Elves applied to them- time passed more slowly in "Underhill," so those who ventured within it often came back decades later; they lack some of the empathy we take for granted, and often did experiments & tricks upon the unsuspecting, either for research or to relieve boredom; they control unusual magic; their alien biology reacted poorly with certain forms of iron and silver. And so forth.
In another campaign, Elves were replaced by 3 kinds of Fey- actually Elves who had recaptured their original nature in order to survive an "extinction level event." One kind were actually sentient plants with lifespans in the 10K+ year range. One kind embraced Shadow- think a melding of Drow & Shadar-Ki and you're on the right track- and were virtually invisible in darkness. The third kind seemed to be connected in some way to the stars, with a natural radiance and the ability to manipulate light.