Lerma River
The Lerma Santiago River (Río Lerma Santiago) is Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

's second longest river. It is a 965 km (599.6 mi) river in west-central Mexico that begins in Mexican Plateau
Mexican Plateau
The Central Mexican Plateau, also known as the Mexican Altiplano or Altiplanicie Mexicana, is a large arid-to-semiarid plateau that occupies much of northern and central Mexico...

 at an altitude over above sea level, and ends where it empties into Lake Chapala
Lake Chapala
Lake Chapala is Mexico's largest freshwater lake. It lies in the municipalities of Chapala, Jocotepec , Poncitlán, and Jamay, in Jalisco, and in Venustiano Carranza and Cojumatlán de Régules, in Michoacán.- Geographic Features :...

, Mexico's largest lake, near Guadalajara
Guadalajara, Jalisco
Guadalajara is the capital of the Mexican state of Jalisco, and the seat of the municipality of Guadalajara. The city is located in the central region of Jalisco in the western-pacific area of Mexico. With a population of 1,564,514 it is Mexico's second most populous municipality...

, Jalisco
Jalisco officially Estado Libre y Soberano de Jalisco is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is located in Western Mexico and divided in 125 municipalities and its capital city is Guadalajara.It is one of the more important states...

. The river is notorious for its pollution, but the water quality has demonstrated considerable improvement in recent years due mostly to government environmental programs and through massive upgrading projects of sanitation works.


The Lerma River originates from the Lerma lagoons near Almoloya del Río
Almoloya del Río
Almolya del Río is a town and municipality located in the State of Mexico 26 km from the state capital of Toluca. It is located 2,600 meters above sea level. The name Almoloya comes from the Nahuatl phrase almoloyán which means place where water flows out...

, on a plateau more than above sea level, and southeast of Toluca
Toluca, formally known as Toluca de Lerdo, is the state capital of Mexico State as well as the seat of the Municipality of Toluca. It is the center of a rapidly growing urban area, now the fifth largest in Mexico. It is located west-southwest of Mexico City and only about 40 minutes by car to the...

. The lagoons receive their water from springs rising from basaltic volcanics that flow down from Monte de Las Cruces. These are located between the Valley of Toluca and the Mexico Basin.

The river forms the short border between the states of Querétaro
Querétaro officially Estado Libre y Soberano de Querétaro de Arteaga is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided into 18 municipalities and its capital city is Santiago de Querétaro....

 and Michoacán
Michoacán officially Estado Libre y Soberano de Michoacán de Ocampo is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 113 municipalities and its capital city is Morelia...

 then flows west-northwest through the state of Guanajuato
Guanajuato officially Estado Libre y Soberano de Guanajuato is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 46 municipalities and its capital city is Guanajuato....

. After turning southward, the river separates Guanajuato and Michoacán, and Michoacán and Jalisco before flowing, after a course of about , into Lake Chapala, west-southwest of La Barca. It has a length of . When it empties into Lake Chapala, the system stands at above sea level.

Some people consider the long Río Grande de Santiago
Río Grande de Santiago
The Río Grande de Santiago is one of the longest rivers in Mexico, measuring up long. The river begins at Lake Chapala and continues roughly north-west through the Sierra Madre Occidental, receiving the Verde, Juchipila, Bolaños, and other tributaries...

, which continues from Lake Chapala northwest towards the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

, to be a continuation of the Lerma River.

Importance in Mexico

During the 17th and 18th centuries, large haciendas were established along this river, including the Atenco ranch, which was founded with bulls that belonged to Hernán Cortés
Hernán Cortés
Hernán Cortés de Monroy y Pizarro, 1st Marquis of the Valley of Oaxaca was a Spanish Conquistador who led an expedition that caused the fall of the Aztec Empire and brought large portions of mainland Mexico under the rule of the King of Castile in the early 16th century...

. The bulls from this area are considered some of the finest stock for bullfighting. The river is dotted with cities such as Lerma, México and San Mateo Atenco
San Mateo Atenco
San Mateo Atenco is a city and a municipality located in the State of México in Mexico. It lies west of the Federal District near the municipality of Metepec, in the central part of the state of México, and is part of the Toluca urban area bordering the city to the east. Atenco is derived from the...

 to small picturesque villages with cultural significance such as Malinalco
Malinalco is a town and municipality located 65 kilometers south of the city of Toluca in the south of the western portion of the Mexico State. Malinalco is 115 km southwest Mexico City....


The Lerma River–Lake Chapala basin is considered to be the most important watershed in the country by the federal government. With its major tributaries, the Laja, Apaseo, and Turbio the Lerma constitutes Mexico's largest river system. The Lerma River is not navigable by water craft, but it is critical to regional agricultural irrigation. In the Lerma River/Lake Chapala watershed, 52,125 of the total 78,000 (roughly 67%) farmers are classified as small farmers. Currently 820,000 hectares are irrigated and an estimated three million hectares are in agricultural production.

The population in the watershed as of 1997 was 9.35 million with an annual growth rate slightly less than the national average. The population is distributed among 6,224 localities; 18 of these have a population greater than 50,000 inhabitants. The rural population is currently 32 per cent. The Lerma's water is also a source for the municipal water supply in the Guadalajara and Toluca metropolitan areas. While water extraction and use has been adequate for the region's larger population centers, rural areas have had chronic problems with access to potable water from the river and the aquifers that feed it. Wells drilled into these aquifers have very low yields.


The Lerma River has had chronic problems with pollution. Most of the problems are due to untreated and under-treated wastewater being discharged into the river. Reservoirs constructed to control the highly varied flow of the river are often choked with water hyacinths due to eutrophication
Eutrophication or more precisely hypertrophication, is the movement of a body of water′s trophic status in the direction of increasing plant biomass, by the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system...

 caused by the untreated effluents. The most important industries in the Lerma River area are those that produce meat, dairy, produce, beverages, pulp and paper, leather goods, petrochemical and chemical products. Little or no emphasis on wastewater treatment and recycling has been imposed upon these economic activities.

The situation became extremely bad in the last 1980s because of erratic water policies that did little or nothing to regulate water use among competing interests and failed to consider the effects of upstream activities to those living downstream. Government plans were drawn up due to intense public pressure leading to improvement of the water quality in the 1990s. By 1997, 45 plants with a treatment capacity of 5.72 m3/s were operating on a regular basis with an average running efficiency of about 70 per cent. Six further treatment facilities were under construction to raise the regional capacity to 9.56 m3/s. In Lake Chapala, into which the Lerma River flows, water quality improved from 90% of the lake having poor water quality in 1989 to 85% of the lake having good quality in 1997. However, the worst water quality was still closest where the Lerma River discharged into the lake.

However, in the decade beginning in 2000, contamination levels of the river system have again become alarming, with studies in Michoacán and Guanajuato documenting an increase in cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

 and neurocisticercosis in populations that live near the river. The Lerma River portion of the Lerma–Chapala basin is considered to be the most polluted, especially in stretches closest to its source near Almoloya del Río. Since 2005, industrial contaminants have become a serious concern as well as the continuing loss of plant life in and around the river itself. In 2005, thousands of fish suddenly died in the river in the municipality of Pénjamo
Penjamo Hidalgo Cradle, is the City head-board of the homonymous Municipality, one of 46 municipalities of Guanajuato's Mexican state. It is one of the cities with major commercial movement of the State, and is considered to be the major City of the Southwest of the entity and the city number 17...

in Guanajuato state when effluent flow depleted the oxygen in that part of the river. The lower parts of the river, closer to Lake Chapala are in better shape because there is less urbanization there.
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