LOS ANGELES — A popular stretch of the San Gabriel River will get a $3.5 million brush-up to improve water quality and access at a key source that provides Los Angeles County with one-third of its water supply, officials announced Tuesday.

The federal funding will help the Watershed Conservation Authority, USDA Forest Service, tribes and community groups conduct trash-removal projects, create new walking trails and install additional restrooms, protecting a watershed within the San Gabriel Mountains National Monument, according to federal, state, tribal and local partners.

The east fork of the river flows through the national monument, which received more than 4.5 million visitors in 2021. That intense level of use, especially on peak days, can lead to excess trash and other management challenges, officials said.

"This collaborative effort is a win-win that will improve an important source of water for Southern California communities, deliver a healthier watershed for native species and enhance outdoor access for millions in the Los Angeles Basin," California Gov. Gavin Newsom said in a statement. "California will continue working with partners across the board to protect and preserve our common home."

This month, the state marked the 10-year anniversary of the national monument, which was expanded by President Joe Biden in May along with the Berryessa Snow Mountain National Monument in Northern California. The action increased protected lands in California by 130,000 acres, authorities said.