Lake Nicaragua or Cocibolca or Granada (Lago de Nicaragua, Lago Cocibolca, Mar Dulce, Gran Lago, Gran Lago Dulce, or Lago de Granada) is a vast freshwater lake in Nicaragua of tectonic origin. With an area of 8 264 km², it is the largest lake in Central America, the 21st largest lake in the world (by area) and only slightly smaller than Lake Titicaca. With an elevation of 32 m (105 ft) above sea level, the lake reaches a depth of 26 m (84 ft). It is intermittently joined by the Tipitapa River to Lake Managua.
The lake is connected to the Caribbean Sea by the San Juan River, historically making the lakeside city of Granada, Nicaragua, an Atlantic port although it is closer to the Pacific. The lake has a history of Caribbean pirates who assaulted nearby Granada on three occasions. Despite draining into the Caribbean Sea, the Pacific Ocean is near enough to be seen from the mountains of Ometepe (an island in the lake).
Before construction of the Panama Canal, a stagecoach line owned by Cornelius Vanderbilt's Accessory Transit Company connected the lake with the Pacific across the low hills of the narrow Isthmus of Rivas. Plans were made to take advantage of this route to build an interoceanic canal, the Nicaragua Canal, but the Panama Canal was built instead. In order to quell competition with the Panama Canal, the U.S. secured all rights to a canal along this route in the Bryan-Chamorro Treaty of 1916. However, the idea of another canal in Nicaragua still periodically resurfaces. Ecocanal is one of these projects.
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. Numerous other fishes live in the lake, including at least 16 species of endemic cichlids. A non-native cichlid, a Tilapia, is used widely in aquaculture within the lake. Owing to the large amount of waste they produce, and the risk of introducing diseases to which the native fishes have no resistance, they potentially are a serious threat to the lake's ecosystem.
Nicaraguans call the Lake Lago Cocibolca or Mar Dulce (literally, Sweet Sea; in Spanish, freshwater is agua dulce). The lake has sizeable waves driven by the easterly winds blowing west to the Pacific Ocean. The lake holds Ometepe and Zapatera which are both volcanic islands, as well as the archipelago of the Solentiname Islands. The lake has a reputation for periodically having powerful, unnavigable storms.
In the past 37 years, considerable concern has been expressed about the ecological condition of Lake Nicaragua. In 1981 the Nicaraguan Institute of Natural Resources and the Environment (IRENA) conducted an environmental assessment study and found that half of the water sources sampled were seriously polluted by sewage. It was found that 32 tons (70,000 pounds) of raw sewage was being released into Lake Nicaragua daily. Industry located along the lake's shore had been dumping effluent for an extended period of time. Pennwalt Chemical Corporation was found to be the worst polluter. Nicaragua's economic situation has hampered the building of treatment facilities nationwide (see: Water supply and sanitation in Nicaragua).