South American snake, also called "water boa” (8)
I believe the answer is:
anaconda
This could be a double definition.
'south american snake' is the first definition.
(anacondas are native to South America)
'called water boa' is the second definition.
'anaconda' can be an answer for 'boa' (anaconda is a kind of boa). I'm not certain of the 'called water' bit.
'also' acts as a link.
Can you help me to learn more?
(Other definitions for anaconda that I've seen before include "Large boa of South America" , "One may put squeeze on" , "Aquatic snake" , "cold-blooded killer" , "The largest snake" .)