Earth Day Cruise. Cruise San Francisco Bay on the wind- and solar-powered Hornblower Hybrid. Tickets $10. 11 a.m.-4 p.m at Pier 33. For more information, call (415) 981-7625 or go to www.alcatrazcruises.com.
Diaper Discovery Day. Busy Bee Bottoms, the Real Diaper Association, Bare Ware Diapers and Martha Bruce will display alternatives to disposable diapers. 10 a.m.-2 p.m., Martha Bruce Photography Studio, 1555 Yosemite, No. 22. www.busybeebottoms.com.
Earth Day Program. "The North Pole Was Here - Imagine," an updated slide show based on Al Gore's film "An Inconvenient Truth." Noon-1:30 p.m., Main Library, Koret Auditorium, 100 Larkin St. For more information, go to: links.sfgate.com/ZGVP.
San Car-less Day and Highlands Park Celebration. Activities feature kite-flying and nature. 1-3 p.m., 2600 Melendy Drive. For more information, call the San Carlos School District at (650) 508-7333.
Mount Tamalpais State Park projects. Trail maintenance, campground restoration, trash removal. 9 a.m.-1 p.m. More information: links.sfgate.com/ZGVQ.
Eastshore State Park projects. Nonnative fennel and acacia removal and pruning of blackberry bushes in Berkeley Meadow. 9 a.m.-noon. More information: links.sfgate.com/ZGVQ.
Earth Day Festival. Tree-planting, discussions and entertainment. 10 a.m.-3 p.m. Barrett Community Center, 1870 Ralston Ave. For more information, call (650) 595-7441 or go to www.belmont.gov/earthday.