Lake Nicaragua

The lake lies in a long, low valley.

Rivers bring water in, and the San Juan River carries water out toward the sea.

Lake Nicaragua sits in the middle of a long valley formed by movements of the Earth's crust. Lake Managua lies upstream in the same valley, and the San Juan River carries water from Lake Nicaragua toward the Caribbean Sea.

IAGLR lists both tectonic forces and volcanic damming as part of the lake's origin. Rain in its basin ranges from about 1,200 millimeters a year in the northwest to about 4,000 millimeters in the southeast.

ILEC describes Lake Cocibolca as occupying the middle section of a tectonic valley shared with two other watersheds: Lake Xolotlán (Managua) upstream and the San Juan River downstream, which links it to the Caribbean. IAGLR gives its geologic origin as both tectonic and volcanic damming.

The lake's own basin covers 23,844 km², 83% in Nicaragua and 17% in Costa Rica. Rainfall averages about 1,200 mm a year at Malacatoya in the northwest and about 4,000 mm in the upper Río Frío basin in the southeast. ILEC's 40-year water balance shows water leaving both through the San Juan River at San Carlos and by evaporation from the lake surface.

Ometepe is an island in the lake. It is made of two volcanoes joined together.

One of the volcanoes is still active.

Ometepe Island is made of two volcanoes, Concepción and Maderas, joined by a low strip of land. UNESCO says Concepción, which is still active, rises to 1,610 meters, and Maderas rises to 1,394 meters.

The island has dry, moist and cloud forests and wetlands. In 2010 UNESCO named it a biosphere reserve, a place that protects nature while people live and work there.

UNESCO's Man and the Biosphere Programme lists Ometepe Island (2010, 53,860 ha) as a biosphere reserve shaped by two volcanoes: Concepción in the northeast (1,610 m, still active) and Maderas in the east (1,394 m). A 2010 note in the journal Oryx describes the 276 km² island as one of the world's largest freshwater islands, with a wetland isthmus between the volcanoes.

Oryx adds that its range of altitudes gives dry, transitional, moist and cloud forests and lowland wetlands, home to the endemic tree Ardisia ometepensis and the endemic salamander Bolitoglossa insularis, first described in 2008. UNESCO says the fog forests have the highest conservation value in Nicaragua.

Some sharks swim all the way from the sea into this lake!

They are called bull sharks.

The ILEC brief says bull sharks, which people there call "freshwater sharks," travel between the Caribbean Sea and Lake Nicaragua. ILEC also names two kinds of sawfish.

The same brief reported signs that these sharks and sawfish were being overfished. On Ometepe, UNESCO lists the yellow-naped parrot and the white-headed capuchin monkey among the endangered animals of Maderas Volcano National Park.

ILEC's brief names three species showing signs of overexploitation: Carcharhinus leucas, locally called the bull shark or freshwater shark because it migrates between the Caribbean Sea and Lake Cocibolca, and two sawfish, Pristis perotteti and Pristis pectinatus.

UNESCO lists the yellow-naped parrot (Amazona auropalliata), the white-headed capuchin (Cebus capucinus) and the smalltooth sawfish (Pristis pectinata) among the endangered fauna of Volcán Maderas National Park, and Oryx notes that Maderas is an Important Bird Area recognized by BirdLife International.

The photo shows waves on the lake.

Near water, always stay close to your grown-up and wear a life jacket on a boat.

The US Centers for Disease Control and Prevention (CDC) says life jackets lower the risk of drowning while boating, and that children should wear them for all activities in and around natural water.

Grown-ups should watch children closely near water. UNESCO notes that Concepción, on Ometepe, is still an active volcano.

The CDC advises that life jackets reduce the risk of drowning while boating for people of all ages and swimming abilities, that children should use them for all activities in and around natural water, and that adults should supervise children closely even when lifeguards are present.

UNESCO describes Concepción, on Ometepe, as still active.