El Junco, Freshwater lake at San Cristóbal Island, Ecuador.

El Junco is a freshwater lake on San Cristóbal Island that fills an extinct volcanic crater high in the island's highlands. The water sits protected within this natural basin, creating a green and calm body of water surrounded by rocks and low vegetation.

The lake formed thousands of years ago as water accumulated within the volcanic crater and remained trapped there. During World War II, American military personnel relied on this water source while stationed on the nearby island of Baltra.

The name El Junco comes from the endemic sedge Cyperus anderssonii that grows beside the water. The lake is the only source of fresh water in Galápagos and made the first permanent settlements on San Cristóbal possible. Today it is managed by the Galápagos National Park Service, and the crater rim is a place to watch the endemic San Cristóbal mockingbird and white-cheeked pintails.

A path circles the shoreline and is generally easy to walk, though certain sections become muddy after rain. Sturdy footwear with good grip and weather-appropriate clothing make the walk more comfortable and safe.

The layers of sediment at the lake bottom form a natural record of climate patterns over thousands of years. This ancient archive helps scientists understand how weather and environmental conditions have shifted across the Galápagos.