The Arroyo Seco Watershed

Arroyo Seco Watershed The Arroyo Seco watershed, stretching from the San Gabriel Mountains to Downtown Los Angeles, has a beauty and charm unmatched in Southern California. Historically a cultural center of the Gabrielinos (also known as the Tongva or Kizh), the Arroyo Seco River now passes through the communities of Pasadena, Altadena, La Cañada-Flintridge, South Pasadena, and Northeast Los Angeles. The Arroyo unites a highly diverse region and serves as the focal point of a shared identity.

Arroyo Seco Watershed Map Geographically, the Arroyo Seco Watershed is a subwatershed of the Los Angeles River Watershed. The basin sits between the San Gabriel Valley to the east and the San Fernando Valley to the west, and water flows out primarily through the confluence with the Los Angeles River.

For many years now, Arroyo lovers have worked hard to protect and restore our wonderful watershed. Up and down the Arroyo, citizens, neighborhood groups, and governmental agencies are collaborating to manage our watershed better for nature and people and to pass on its splendor to future generations.

On this page, you will be able to learn more about the Arroyo Seco Watershed and why it is so important to preserve it for ourselves and future generations.

What is a watershed?

Watershed Diagram

A watershed is that area of land, a bounded hydrologic system, within which all living things are inextricably linked by their common water course and where, as humans settled, simple logic demanded that they become part of a community.
—John Wesley Powell

Watersheds, also known as drainage basins, are geographical features that delineate the flow of water. Much like a bathroom sink, all water that enters the basin will flow to a point where it leaves, while water that falls outside the basin will flow elsewhere. Because of this, things within a given watershed have an important relationship with one another.

Stream or Storm Drain?

This is the first question many people ask when the first see the Arroyo Seco. The Arroyo Seco, Spanish for dry stream is a natural river spanning 22 miles. A concrete channel was installed in the 1930s and 1940s, giving most of it the appearance of an artifical canal, and in fact, the Arroyo is currently to remove stormwater from our watershed. However, the Arroyo Seco is a historically important site going back thousands of years and is home to a rich variety of natural habitats. While things have changed in recent decades, the possibility of restoring it has not been lost!

Restoration Goals

  • Restore the natural hydrological functioning of the watershed
  • Better manage, optimize, and conserve water resources while improving water quality
  • Restore, protect and augment habitat quality, quantity and connectivity
  • Improve recreational opportunities and enhance open space

See our planning page for more information on studies and projects in the Arroyo Seco Watershed.

The Arroyo Seco Watershed Coordination Program

The Arroyo Seco Watershed Coordination Program, sponsored by the Arroyo Seco Foundation, is part of a statewide effort by the California Department of Conservation and is funded by the CALFED Bay Delta Authority. The program is designed to improve the capacity of local residents, organizations and agencies to better manage and improve the Arroyo Seco Watershed. The key goals are to promote water conservation, improve water quality, and community and institutional partnerships to accomplish these goals. For more information, please contact the Watershed Coordinator

Corps Ecosystem Study Is Initiated

The Arroyo Seco Watershed Feasibility Study, a partnership between the U.S. Army Corps of Engineers and the County of Los Angeles Department of Public Works, with the assistance of governmental agencies and environmental organizations within the watershed, was officially launched October 26, 2005. This was intended to be a three-year study to explore solutions for water resources, conservation, habitat and environmental restoration issues within the Arroyo Seco Watershed. Despite the strong support of local communities, the study has lagged because it has only received minimal federal funding despite the diligent efforts of Congressman Adam Schiff and Senator Dianne Feinstein.

We still have great hopes for the Corps study to provide a lot of answers regarding the sustainable management of the Arroyo Seco Watershed.

News Coverage.

Study Plan


Ten Things You Can Do to Make a Difference in Your Watershed

Here is a handy guide to how you can learn about the Arroyo Seco Watershed, become active in watershed protection programs, and help increase public awareness.

How to Make a Difference