Black Rock Rearing Ponds were artificially created by the City of Los Angeles by building a dam for diversion purposes near the source of Black Rock Springs. The springs normally have a flow of from 12 to 15 cfs at a temperature of 59 F. The proposal to rear large numbers of fish in such large ponds was at first frowned upon by some of the Department's hatchery personnel.
The ponds were first operated in the fall of 1941, when 450,000 rainbow fingerlings were placed in the ponds. During the spring of 1942, 274,385 trout averaging over 5 inches in length and weighing over 36,000 pounds were planted from the ponds. This production removed any doubt regarding their fish rearing possibilities.
In 1976 the hatchery was expanded by addition 2,000 feet of concrete raceways. The old rearing ponds were utilized as broodstock ponds until 2012 when the hatchery ceased spawning activities.