Opened in 1925 in a spot adjacent to what is now the San Francisco Zoo (Sloat Boulevard and Great Highway), it was (at 1,000 feet long) the largest pool in the United States. Water was pumped in directly from the ocean. It closed down in 1972.
Related material on other sites
An interesting history of Fleishhacker Pool, and some contemporary photos of the inside of its bath house structure at Terrastories.com