Lerma River

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The Lerma Santiago River (Río Lerma Santiago) is Mexico's longest river. It is a 2,600-km-long (2,250-mile-long) river in west-central Mexico that begins in Mexico's central plateau at an altitude over 3,000 meters above sea level, and ends where it pours into the giant Lake Chapala (at 1,510 meters above sea level), near Guadalajara, Jalisco. The river is notorious for its pollution, but the water quality has demonstrated considerable improvement in recent years due mostly to government environmental programs.

1 River's Path
2 Importance in Mexico
3 Pollution
4 Sources

[edit] River's Path

The Lerma River originates from the Lerma lagoons near Almaloya del Río, on a plateau 2,600 meters above sea level, and 24 km southeast of Toluca. The lagoons receive their water from springs rising from basaltic volcanics that flow down from Monte de Las Cruces.

The river flows northwestward through México State. The river defines the short border between the Mexican states of Querétaro and Michoacán, and then continues mostly northwest through Guanajuato. Then it loops south where it defines the border between Guanajuato and Michoacán, then between Michoacán and Jalisco, after which the Lerma enters Lake Chapala.

Some people consider the 400-km-long Río Grande de Santiago, which continues from Lake Chapala northwest towards the Pacific Ocean, to be a continuation of the Río Lerma. If Lake Chapala were to overflow, the excess water would flow into the Río Grande de Santiago, but this has not occurred since 1977.

[edit] Importance in Mexico

The Lerma River is not navigable by water craft, but it is critical to regional argicultural irrigation, and its flow powers several hydroelectric plants.

The Lerma's water is also a source for the municipal water supply in the Guadalajara metropolitan area.

[edit] Pollution

The Lerma's historic reputation for polluted water has been partially mitigated by extensive government environmental programs. The Lerma River basin now has 44 wastewater treatment plants to help reduce toxic runoff into the Lerma.

Another environmental threat is overuse of the Lerma's water supply, which has led to a decrease in Lake Chapala's water level, and threatens the Lake Chapala Lerma River watershed aquifers.