5 min read
© Jaime Rojo/Natural Numbers

Under this innovative approach to legally protect river flows, Mexico is securing water for the future—even in the face of climate change.

Water Reserves protect the volume of water in almost half of Mexico’s 756 river basins, representing 55% of the country’s surface water. They support the health and protection of 82 Natural Protected Areas, 64 Ramsar wetlands and Mexico’s last 4 free flowing rivers.

As the climate changes, especially in the face of longer and more intense dry seasons, Mexico faces increased water security risks. Legally protecting the flows and ecosystem services of the San Pedro Mezquital helps address water security issues and adapt to climate variability. Through a water reserve, a percentage of mean annual runoff is guaranteed, which can be used to buffer climate impacts and help to manage risks. 

The San Pedro Mezquital was the first Environmental Water Reserve designated by Mexico with around 80% of its mean annual runoff allocated to ensure water and nutrients are supplied to the Marismas Nacionales.

© Jaime Rojo/WWF

"Water reserves matter because they secure freshwater for nature and drinking water for people. From Cape Town South Africa, to California, communities are suffering when watersheds run dry. Policies like these are needed more than ever. Mexico’s network of water reserves stands as a model for other countries to follow in securing their own watersheds before it’s too late."

- Carter Roberts, President and CEO of WWF-US

© Jaime Rojo

San Pedro Mezquital 

The San Pedro Mezquital is the last healthy, well-connected portion of river in Mexico’s western Sierra Madre Mountains, flowing into the Pacific Ocean. During the rainy season, the river swells with runoff, inundates the floodplain, and supplies the water and nutrients to Marismas Nacionales, a National Wetlands, Biosphere Reserve and Ramsar site, and home to 200,000 hectares of mangrove forests. High flows spread across its floodplain, depositing nutrient-rich sediment, creating fertile land when the river is low. The San Pedro Mezquital’s ebbs and flows support the agriculture and fisheries that sustain the surrounding 432 local communities, and more than 100 species of flora and fauna that are under protection. 

© Jaime Rojo/WWF
© Thor Morales / WWF Mexico


The Usumacinta is the largest and most biodiverse river in Central America, and one of Mexico's last remaining free-flowing rivers. As of June 2018, a water reserve protects 93% of the water in the river. Along with securing water for the forests and species along the rivers, including the iconic jaguar, the water reserve also strengthens two previous conservation decrees that promote the sustainable use of forest resources and prohibit exploration for oil and gas. The water reserve also protects important livelihood activities for basin inhabitants, such as aquaculture, seasonal agriculture and tourism.

© Jaime Rojo/WWF

Water Reserved for All 

This Reserve decree outlines three types of reserves: one for domestic use, another for hydropower generation, and the third for the environment. The Environmental Water Reserve is included in the management program of Marismas Nacionales, and regulates any water-related infrastructure that is proposed. Therefore, before construction can be authorized, projects must prove that they will not exceed the Environmental Water Reserve and negatively affect flow to the Marismas Nacionales. In addition to environmental flow requirements, other conditions placed on development within a Reserve include sediment parameters and protection of social resources related to Indigenous People’s rights and land (cultural sites), among others.  

What is a water reserve? 

In order to safeguard important ecosystems, maintain invaluable ecological services, and adapt to water scarcity in a changing climate, Mexico established a National System of Water Reserves in 2012. This was a collaborative process undertaken by the National Water Commission of Mexico (CONAGUA) in partnership with the WWF-Gonzalo Río Arronte Foundation Alliance, together with the National Commission of Natural Protected Areas. The process involved calculating the water requirements of critical ecosystems, implementing a national standard for determining environmental flows (the water regime provided within a river to maintain ecosystems and their benefits), identifying priorities for conservation, and establishing water reserves.  

A water reserve is the volume of water that is excluded from the total amount to be allocated to various management purposes. It is the legal amount for conservation or restoration of vital ecosystems, including maintenance of the functionality of the water cycle and its environmental services, and as a means of providing a reserve in a changing climate. Specific protections include those that protect environmental flow requirements of a river and its ecosystem. 

Water reserve decrees ultimately aim to guarantee water security in Mexico for the next 50 years within a highly variable climate. 

© Jaime Rojo