Lake Merritt in central Oakland began as an arm of San Francisco Bay where creeks met broad wetlands used by the Ohlone and later incorporated into Rancho San Antonio. After the Gold Rush, the polluted San Antonio Slough was transformed in 1868 when Mayor Samuel Merritt funded a dam that reduced tidal exchange and created a more stable salt-water lake. In 1870, protection for birds on the remaining wetlands established the Lake Merritt Wildlife Refuge, the first official wildlife refuge in the United States. Reshaped by dredging, park design, and civic improvements, it remains a historic urban sanctuary, park, and defining Oakland landscape.