There are 2 species of crocodile in Australia: the native salt water (estuarine) crocodile and the endemic Australian freshwater crocodile. The difference between these species is their size, location, and threat to humans.
Both species live in the tropics of Australia, but Salt water crocodiles live in and near coastal areas, and only further inland via rivers that flow out to the coast. For this reason. they sometimes coexist in areas with fresh water crocodiles. As the name suggests, fresh water crocodiles live in fresh water, so they are typically found in rivers, lakes, and waterholes, but rarely in saline water.
Both types of crocodile are protected in Australia. This is important because freshwater crocodiles are only found in Australia, while salt water crocodiles are a threatened species in both Asia and Africa where they also exist. Salt water crocodile pose a serious threat to people, while freshwater crocodiles are much less dangerous.