Human Impacts

The main negative impact people have on Lake Nicaragua is through pollution. Many large cities send their residential and industrial sewage to the lake. Even cities that are far away from the lake dump their sewage into rivers that lead to the lake. In 1981, MARENA (Ministry of the Environment and National Resources) found in a study that 70,000 pounds of raw sewage were being dumped into the lake a day. During this time, the Sandinista government was putting no money into the sewage and water infrastructure. However, between 2002 and 2007, ENACAL (Nicaraguan Water and Sewage Enterprise) invested 162 million dollars into the country’s water and sanitation systems.

Nicaraguan investment per capita in water supply and sanitation

Source: Unidad Pública de Inversiones; Data on population and deflators: World Bank World Development Indicators database

            The most infamous resident of Lake Nicaragua is the Bull Shark. Originally thought to be an endemic species of Lake Nicaragua, the Lake Nicaragua shark (as it is often called) recently was found to be nearly identical to Bull Sharks in other locations and to have entered the lake via the San Juan River. Because of the sharks’ aggressive nature, fisherman hunted these sharks to near extinction during the time of the Somoza Dynasty’s rule in Nicaragua (1936-1979). Today, the sharks are known more as legends due to how rare they are. The last media report of a sighting was in the year 2000. As far as wildlife in general, the dual-volcanic island of Ometepe was recently named an UNESCO Biosphere Reserve. The island has hundreds of species of birds as well as the more than 40 species of fish that reside in the lake. In addition to the bull shark, another notable marine animal that occupies the lake is the sawfish. The lake is inhabited by 16 species of cichlid fish. The cichlid population began to drop due to an attempt to increase fishing yields in the 1980s with the introduction of the farming of African tilapia fish. In 1995, cichlid were estimated to account for 58% of the lakes biomass, but this figure has likely to have dropped do to heavy fishing of these species as well as competition with the tilapia.