Here's another interesting article from AO about the Ahuizotl.
"The Ahuizotl (which may be translated from Nahuatl to mean ‘Thorny One of the Water’) is a creature found in the mythology of the Aztecs. This legendary creature is believed to inhabit the lakes and rivers around Tenochtitlan, the capital of the Aztec Empire. The Ahuizotl is said to have been a malevolent creature whose victims were often fishermen, and people who wandered too close to the edge of the waters. There has been some debate as to whether the Ahuizotl is, in fact, a real creature or not, and if it is real, whether it has relatives that still survive today."