Every day, millions of Bay Area residents look out at the San Francisco Bay from their homes, their cars and from airplane windows. But they rarely get out and walk its shorelines, paddle a boat across its surface or wade into its waters.

Hoping to connect more people to the aquatic landmark that gives the region its name, environmentalists, political leaders and nonprofit groups on Saturday will hold the first-ever “Bay Day,” an all-day event they hope will become an annual tradition.

Roughly 40 events are planned in all nine Bay Area counties at which the public will be encouraged to hike, ride bicycles and kayak on and around the bay, and learn about and celebrate its remarkable features and wildlife.

“The goal is to make this an annual day, like Earth Day for the bay,” said David Lewis, executive director of Save the Bay, an environmental group based in Oakland that is organizing the overall effort.

A full list of the activities — many are free, but some of require registration ahead of time — is at www.bayday.org.

Among them: A cleanup of wetlands and marshes in the Alviso area with volunteer kayakers, guided public bike rides from Berkeley and San Leandro to bayfront trails, volunteer wetland restoration at Bair Island in Redwood City and guided walks along the Sonoma bayfront.

“Everybody is welcome. Bring your helmet; bring your bike,” said Ginger Jui, a spokeswoman for Bike East Bay, a nonprofit group that is hosting two rides to the Alameda County shoreline. “It’s a great time to meet other people who are interested in the bay.”

Apart from recreational activities with family members, organizers hope that if more people experience the bay firsthand, more people will care about it.

“We know that people love the bay, but most of the time they take it for granted,” said Lewis. “The best protection for the bay as it faces new challenges in the coming decades, like sea-level rise and stormwater pollution, is for people to be in touch with it and experience it. We’re hoping this will be an annual opportunity to spread awareness about what the bay needs from people.”

San Francisco Bay is the largest estuary on the West Coast. It drains roughly 40 percent of California’s land and is home to a wide variety of species, from sharks to salmon and bat rays to snowy egrets. But it is also home to 7 million people, eight bridges and numerous factories and wastewater treatment plants that empty into it. Between the 1850s and 1960s, the bay shrunk by one-third due to diking, dredging and filling for farming, airports, highways and development, like Foster City.

Nearly all the filling ended with modern environmental laws, like the Clean Water Act, starting in the 1970s, and in recent years major restoration efforts on thousands of acres have gradually helped bring back wetlands and wildlife. But the bay faces new threats from sea-level rise, diversion of fresh water, plastic pollution, stormwater pollution and invasive species.

Bay advocates won a major victory in June, when Measure AA, a $12 annual parcel tax in all nine Bay Area counties, won voter approval with 70 percent of the vote. That measure will raise $500 million over the next 20 years to restore former industrial salt ponds back to healthy marshes for birds, ducks, harbor seals and other wildlife, along with increasing flood protection for businesses and homes that are threatened as the bay slowly rises from climate change.

“We’ve got much to celebrate with recent success of Measure AA and preserving wetlands from future development, but we have a lot of work still to do,” said San Jose Mayor Sam Liccardo.

Liccardo, who broke his foot recently while running and had surgery on Friday, said he’s trying to figure out which events he can join.

“My wife’s trying to get me in a kayak,” he joked. “Assuming I have my doctor’s permission, I hope I’ll be out there with everybody else.”