Lake Chapala

Lake Chapala is the largest freshwater lake in Mexico.

It has held this title since Lake Texcoco dried up in the early 17th century. The lake sits on the border of two Mexican states, Jalisco and Michoacán. It is located southeast of the city of Guadalajara. The water surface sits at an elevation of 1,524 metres above sea level. This large body of water is part of a young geological area on the American continent.

The lake functions through a complex system of incoming and outgoing water. Four main rivers feed the lake: the Río Lerma, Río Zula, Río Huaracha, and Río Duero. Historically, the Río Grande de Santiago drained the lake. This river carried water northwest toward the Pacific Ocean. However, no water has flowed out of the lake for over 30 years. This change happened because the supply of water from the Lerma River fell significantly.

Lake Chapala has specific physical dimensions and features. It is a shallow lake with a mean depth between 2 and 8 metres. Its maximum depth reaches 12 metres. The lake measures approximately 12.5 kilometres from north to south. Within the water, there are three distinct islands. Isla de los Alacranes is very visible from the town of Chapala. Isla Mezcala is the largest island and contains an old Spanish fort and a Mexican prison. A very small island named La Isla Menor sits next to Isla Mezcala.

Scientists have worked to understand the history of this landscape. They used carbon-14 dating on wood samples found in the lake sediments. These samples show the lake is approximately 38,000 years old. This places its origin in the late Pleistocene, a geological epoch from 1,000,000 to 25,000 years ago. Surrounding the water are many mountain ranges. These include the Sierra San Juan Cosalá and the Sierra del Tigre. These mountains help define the basin where the lake sits.

The ecology of the lake is currently facing serious challenges. The city of Guadalajara has used the lake as a primary water source since the 1950s. Increased urban water consumption caused levels to drop rapidly after 1979. Deforestation near the lake and the Lerma River has caused more sediment to wash into the water. This process, called sedimentation, makes the lake shallower. Shallower water warms up more easily, which increases evaporation. Additionally, municipal, industrial, and agricultural wastes pollute the water. In 2004, the Global Nature Fund named it the "Threatened Lake of the Year."

These environmental changes affect many unique species. The pollution and warmer water have helped invasive water hyacinth grow quickly. This has harmed the fish stocks, including endemic species like certain Chirostoma. Some of these fish are now near extinction. The lake is still a vital habitat for migratory birds. In 2011, researchers recorded about 173 different bird species there.

Many animals are endemic, meaning they are found only here. This includes the Chapala chub and the obscurus subspecies of the Mexican garter snake.

Human communities are deeply connected to the lake's history and scenery. Many towns sit along the coast, such as Chapala, Ajijic, and Jocotepec. Westerners have been interested in the area since Spanish conquistadors arrived in 1530. Tourism grew during the 19th and 20th centuries. Since the 1950s, many retirees from the United States and Canada have moved to the area. There are now an estimated 30,000 foreign residents living along the shores. The health of the lake remains a major concern for both local people and the scientific community.