In Argentina, many eye witness account talk about a giant water snake named Nahuelito, after the name of the lake where it was spotted, Nahuel Huapi lake. Featuring a long swan-like neck and a serpentine snake, that creature has a lenght range from 15 to 150 feet. It can't be seen in any other season than summer.
This monster, reported with fins and humps, annonces its appearances with sudden swells of water or swooshing spray.
Among the reports, there is one of a track of crushed vegetation leading to the lake shore. In the middle of the lake, Nahuelito was lurking. This story was reported in 1922 to Dr. Clemente Onelli, dir. of the Buenos Aires zoo.
Interested by this report and by some other from 1897, he decided to take expeditions. These unsuccesful researches were led by the zoo surintendant, Jose Cihasi.
Since many of the theories link it to a plesiosaur, like Nessie or Champ, I really doubt it (just like Nessie and Champ by the way). This creature could be a relative to the Anaconda, genus Eunectes, or being a giant relative of the water serpents, Hydrophiidaes. Fins can either be some larger parts of the body, without being fins really, or simply being an imaginary thing done by someone who was firmly convinced to see a plesiosaur. But I don't doubt of the credibility of the reports, I simply gives my thoughts.
SOURCES:http://www.forteanfieldguide.com/aquatic/nahuelito.html
Cryptozoologix 2001
