The science-fiction TV series Sanctuary features the sanctuary of the title being a place of protection and healing for various supernatural creatures. Merfolk appear very briefly among the creatures of this world, first in the pilot where a mermaid is among the first non-human inhabitants of the sanctuary to be shown. Then in the ninth episode of season one, "Requiem", Dr. Helen Magnus and her protégé Dr. Will Zimmerman travel out to the Bermuda Triangle in a submarine to investigate the merfolk's home, only to find that something mysterious happened out there that tragically killed all the merfolk.
The merfolk's appearances are tantalizingly brief. In the show's original pilot webisode the mermaid have darker skin and more dramatic fins, while in the reshot-for-television pilot they're slightly different, with more subdued fins but with a shock of kelp-like hair. In this universe merfolk communicate telepathically, which is how Dr. Magnus' resident mermaid, nicknamed Sally, felt that something was wrong with her kin out in the wild.
Shoutout: In "Requiem", Helen learns that Will nicknamed their mermaid because her natural name is unpronouncable for them, and that "Sally" is less typical than certain other names, such as "Ariel".