The Lake Merritt BART station is located at Madison St. and 9th St. in the Chinatown/Laney neighborhood. It is across the street from Madison Park.
San Francisco/Fremont, Richmond/Fremont, and San Francisco/Dublin lines run through this station. The station has parking, bike lockers, and indoor bike racks.
Find more info on the official Lake Merritt site: http://www.bart.gov/stations/lake/index.aspx