Why do alligators survive in freshwater, but some crocodiles live in saltwater too?

Crocodilian species differ in how well they regulate salt balance. Saltwater crocodiles possess specialized salt glands that help excrete excess sodium, allowing them to spend time in brackish and marine environments. Alligators, by contrast, are much more restricted to freshwater habitats because their salt balance systems are less effective in high-salinity water. This is why distribution maps often show alligators inland and crocodiles in a wider range of watery habitats. The contrast is a good example of physiology shaping geography.