John Muir came to San Francisco in l868. He stayed just a day. He wanted to go “somewhere wild,” and he took a couple of weeks and walked from the city to Yosemite. He fell in love with what he called California’s “range of light.”

About a hundred years later, when I was a young actor, I took a couple of weeks and walked from San Francisco to Big Sur. I fell in love with California’s nature, too. I’ve tried to be an environmental activist ever since.

A few years ago, I had the honor of narrating an Emmy Award-winning television series about the history of San Francisco Bay. Making that four-hour series taught me a lot. We had beautiful footage of the beauty and diversity of the wildlife that live around the bay. We told the history, from the Gold Rush days when the bay was filled with abandoned sailboats.

We included the booming development and the filling of the bay. In the 1950s, the developers had bay fill plans that would have turned the bay into just a broad river. The most grandiose of all the land speculators’ schemes was to scrape off the top of San Bruno Mountain, build condos on the newly flattened mesa, and conveyor-belt the dirt to fill in the bay and build more houses on the fill.

The last episode in the series was about three Berkeley women, Sylvia McLaughlin, Catherine Kerr and Esther Gulick, who in 1961 founded Save San Francisco Bay. They wanted lots of members; it only cost $1 to join. The organization bloomed into a movement to halt the rampant development and dumping and burning of garbage in the bay.

People all around the bay rose up to support them in protecting and restoring the wetlands. It was to the voters’ good credit — since then, no one even tries to get elected around the bay unless they have strong environmental policies and principles. But the struggle continues.

In 2009, agribusiness giant Cargill applied to use the marshlands, just south of Redwood City, to build 12,000 new residences and 1 million square feet of office space. There was so much public outrage, Cargill Salt withdrew the application.

A few months ago, the Trump administration’s Environmental Protection Agency administrator in Washington changed a preliminary determination of the San Francisco EPA office, declaring that the 1,360-acre site is not subject to the Clean Water Act. Cargill has quickly followed with an announcement that it intends to “explore future uses.”

Locating 30,000 more people in the path of sea-level rise, right next to an already gridlocked freeway doesn’t make environmental or economic sense.

All these years later, Save the Bay, in an unprecedented coalition with Committee for Green Foothills, Baykeeper, and Citizens Committee to Complete the Refuge are challenging this issue in court. David Lewis, executive director of Save the Bay called us all to action: “The bay and wetlands deserve federal legal protection from pollution and development. We won’t let the Trump Administration invite developers to pave the bay.”

On Tuesday, Joe Cotchett, the attorney representing the coalition of citizen environmental groups filed a lawsuit challenging the EPA ruling. “This is one more Trump attack on our environment and San Francisco Bay in the name of profit, which is this administration’s sole consideration in leading our country.”

I am proud to add my name to the list of people, including over 60 elected officials and organizations who have already signed letters of support. Congratulations to all those Bay Savers and “Bay Saviors” for your perseverance to protect what the Spanish explorers called, “the harbor of all harbors.”

Robert Redford is an actor, director and co-founder of the San Francisco-based Redford Center, with his son James Redford.