Why are there sharks in Lake Nicaragua? ?

Question

I have read that there is a kind of bull shark that lives only in Lake Nicaragua. How did they get there? How do they live there? And why?

Answer 1

How they live there -> Bull sharks are able to live in freshwater more easily than other shark species.

How they got there ->  (Is there a river connected to this lake?) Bull sharks can swim up river.

Why -> Because they do apparently   xD;  Do sharks need a reason to live where they do?  This species may have just adapted to living in the lake specifically.

Answer 2

Lake Nicaragua, despite being a freshwater lake, has sawfish, tarpon, and sharks. Initially, scientists thought the sharks in the lake belonged to an endemic species, the Lake Nicaragua Shark (Carcharhinus nicaraguensis). In 1961, following comparisons of specimens, the Lake Nicaragua Shark was synonymized with the widespread Bull shark (C. leucas), a species also known for entering freshwater elsewhere around the world. It had been presumed that the sharks were trapped within the lake, but this was found to be incorrect in the late 1960s, when it was discovered that they were able to jump along the rapids of the San Juan River (which connects Lake Nicaragua and the Caribbean Sea), almost like salmon. As evidence of these movements, bull sharks tagged inside the lake have later been caught in the open ocean (and vice versa), with some taking as little as 7-11 days to complete the journey