Quick answer
Alviso Marina is a 20-acre bayside park at the southern tip of San Francisco Bay in San Jose, and the main gateway to the Don Edwards San Francisco Bay National Wildlife Refuge, the nation's first urban wildlife refuge. The surrounding town of Alviso, incorporated in 1852, was once San Jose's port.
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The Bottom of the Bay
Alviso is thirteen feet below sea level — the lowest point in the Bay Area — sitting at the very bottom of San Francisco Bay. That position once made it a working port: in 1852 it became the first chartered city in California, and steamboats ran from its docks up the bay to San Francisco, carrying the grain and hides of the Santa Clara Valley. The railroad passed it by in 1864, and the port shrank to nothing. What never left was the water. The town flooded repeatedly through the twentieth century, most recently in 1983 and 1995; in 1983 parts of Alviso sat under ten feet of it.
A Gateway to the Refuge
The old shoreline is now Alviso Marina County Park — twenty acres of boardwalk, picnic tables and a boat launch, and the front door to the Don Edwards San Francisco Bay National Wildlife Refuge. The refuge is the nation's first urban wildlife refuge: thirty thousand acres of salt ponds and marsh running up the South Bay. The ponds were built for the salt industry; the old Cargill ponds are being converted back to wetlands, and some still run pink, colored by salt-loving algae and bacteria that thrive in the brine. More than 280 species of birds have been recorded on the refuge, and during migration the ponds crowd with shorebirds.
What to Do
Start at the park by the marina and take the flat trail along Alviso Slough; within minutes the city is behind you and the pond flats run to the horizon. Bring binoculars — in winter the ponds hold thousands of ducks and shorebirds, and the levees put you at eye level with them. The trail is the levee itself, and the refuge rules are simple: stay on it, keep dogs and drones away, and do not step toward the pond edge. Walk out to the end of the boardwalk at low tide, wait for the pink pond to catch the light, and watch the birds work the mud.