The Nuttall Encyclopedia
A fabulous marine monster, said to haunt the lagoons of the Amazon, and to suck into its mouth and swallow whatever comes within a hundred yards of it; before bathing in a lagoon, where he apprehends its presence, the Indian sounds a horn, the effect of which is to make it reveal itself if it is there.
Wood, James, ed. Entry for 'Yacu-Mama'. The Nuttall Encyclopedia. https://www.studylight.org/encyclopedias/eng/nut/y/yacu-mama.html. Frederick Warne & Co Ltd. London. 1900.