Lake Nicaragua Bull Sharks

The lake is famous for one biological oddity: it contains bull sharks, the only true freshwater shark population in the Americas. They reach the lake by swimming up the Río San Juan from the Caribbean, navigating rapids that sailors once thought impassable to any large fish. Sightings in the lake itself are now rare — overfishing of sharks for their fins in the 1960s and 70s collapsed the population — but the occasional dorsal fin still cuts the water near Granada and around Ometepe.

You will not see one. Modern visitors swim in the lake without trouble, locals included. The fishery is still in slow recovery, and conservation programmes on the Río San Juan are trying to protect what remains. The story matters as biology, not as a warning: the lake is huge, the sharks are few, and the chance encounter would be a privilege rather than a danger.

things to do sight
A story
Until tagging studies in the 1960s, biologists believed the lake's bull sharks were a landlocked freshwater species, trapped after the lake separated from the Pacific. Tag-and-recapture work proved otherwise: sharks tagged in the lake turned up in the Caribbean, swimming the rapids of the Río San Juan in both directions. They are the same Carcharhinus leucas as the open-ocean species, simply better at salt regulation than anyone realised.