Seems that human folks has got a kind o’ relation to sech water-beasts – that everything alive come aout o’ the water onct, an’ only needs a little change to go back agin. Them things told the Kanakys that ef they mixed bloods there’d be children as ud look human at fust, but later turn more’n more like the things, till finally they’d take to the water an jine the main lot o’ things daown har. An’ this is the important part, young feller – them as turned into fish things an’ went into thre water wouldn’t never die. Them things never died excep’ they was kilt violent.
Lovecraft, The Shadow Over Innsmouth