Lake Merritt

Lake Merritt was a large tidal lagoon in San Francisco Bay that was dammed off as Oakland grew as a city. It is 155 acres in size, and it was the first official wildlife refuge in the USA in 1870. It has walking and biking trails and parks all around it.

Lake Merritt, in the center of Oakland, was a large tidal lagoon of San Francisco Bay that was dammed off as Oakland became more urbanized in the late 19th century. In 1870 it was designated as the United States' first official wildlife refuge. It is surrounded by parkland and city neighborhoods, with a popular 3.4 miles (5.5 km) walking and jogging path around its 155 acres (63 ha) expanse of water. A bike trail is officially only on the eastern shore.
There is more information at en.wikipedia.org/wiki/Lake_Merritt
www2.oaklandnet.com/government/o/opr/s/LakeMerritt/index.htm