what sort of habitat does it select to live in?
It seems to choose clear, black waters with rocky or sandy bottoms
Giant otter
 The giant otter seems to choose clear, black waters with rocky or sandy bottoms over silty, saline, and white waters. 
what is giant otter? It is a South American carnivorous mammal. where did it get the name from? Giant otter" translates literally as "nutria gigante" .and "lontra gigante" in Spanish and Portuguese which family does it belong to? Weasel family
wiki:18404884
Giant otter [SEP] Habitat
Other researchers suggest approximately and note a strong inverse correlation between sociality and home range size; the highly social giant otter has smaller home range sizes than would be expected for a species of its mass. Population densities varied with a high of reported in Suriname and with a low of found in Guyana.