Nagas are snake-like creatures from the legends of India, and the term is applied to merfolk and Weresnakes as well. In this case, the use of the term in question is as in 'Monster Water-serpent.'
The Naga-Sea-monsters and Freshwater-monsters are reported from all over the orient and in many cases they are distinctly parallel to Chinese dragons. On the other hand, Chinese legend also recognises monster serpents as distinct from the dragons, and so those are more like the limbless Nagas. The Nyans of Burma are likewise merely another local form of Nagas.
The point I am making here is that the reports do NOT describe big snakes; they do not undulate in the serpentine side-to-side manner. They are in fact the same as the more northerly sea-serpents and supposedly undulate up-and-down, producing the 'String-of-buoys' effect, reported as anywhere from several yards to a few hundred feet long. Doubtless this is the effect of waves in a wake (and because of that it has nothing to do with whatever creature might be making the wake, or tell us anything about what its shape might be under the water)
The same 'Giant Serpent' reports are worldwide in the tropics: one article in Fate magazine stated that the immense legendary South American Water-monster Serpent Siucuriju Gigante was also reported in Africa, the Phillipines, and in Australia. And so the same types of reports are indeed all over the southern regions. But they are all actually the same as the more northerly sea-serpents, and the terms should be understood as synonymous. Sea-serpents are world-wide. and their characteristic reported form is the result of a wave action, which has nothing whatsoever to do with the shape of any creature that might be making the waves in its wake. As a matter of fact there is very good documentation that several different animals can create the effect, as well as boats and sometimes natural waves that are not even generated by a live animal at all.
In other words, the names 'sea-serpent', 'naga', 'Sucuriju Gigante', or whatever, do not name any specific animal species, they are all describing an illusion created by a standing wave action and only INTERPRETED as being the body of a long animal undulating vertically on the surface.