Humboldt Bay is a natural bay and a multi-basin, bar-built coastal lagoon located on the rugged North Coast of California, entirely within Humboldt County, United States. It is the largest protected body of water on the West Coast between San Francisco Bay and Puget Sound, the second-largest enclosed bay in California, and the largest port between San Francisco and Coos Bay, Oregon. The largest city adjoining the bay is Eureka, the regional center and county seat of Humboldt County, followed by the city of Arcata. These primary cities, together with adjoining unincorporated communities and several small towns, comprise a Humboldt Bay Area with a total population of nearly 80,000 people. This comprises nearly 60% of the population of Humboldt County. The bay is home to more than 100 plant species, 300 invertebrate species, 100 fish species, and 200 bird species. In addition, the bay and its complex system of marshes and grasses support hundreds of thousands of migrating and local shore birds. Commercially, this second-largest estuary in California is the site of the largest oyster production operations on the West Coast, producing more than half of all oysters farmed in California.

The North Coast of California is a region in Northern California that lies on the Pacific coast between San Francisco Bay and the Oregon border. It commonly includes Mendocino, Humboldt, and Del Norte counties and sometimes includes Lake and two counties from the San Francisco Bay area, Marin and Sonoma.