Damned hipster mermaids.

Fresh-water mermaids were not as beautiful, by most human's standards, as their more exotic salt water cousins. The humans wanted brightly-colored hair and glistening fins. But the fresh-water tribes were far more subtile than that. They blended with the earthy tones at the water's edges and were far too good at hiding. It was why they had not been nearly destroyed by the fishing industry. It was why their culture, though muddy, thrived. It's why their art and music was revered inland, even if humans didn't realize what it was. It's why you've never heard of them