The Santa Ana River Mainstem Project is located along a 75-mile reach of the Santa Ana River in Orange, San Bernardino and Riverside counties. The improvement plan includes Seven Oaks Dam (145,600 acre-feet), management of overflow area-Seven Oaks to Prado (35 miles); raise Mill Creek levee (2.4 miles); additional storage at Prado (140,600 acre-feet); improvements along Oak Street Drain/Riverside County (3.6 miles), Santiago Creek/Orange County (1.2 miles) and lower Santa Ana River (31 miles); recreation development; mitigation and preservation; and San Timoteo (5.4 miles).
The various projects within the Santa Ana River Mainstem were authorized under the Water Resources and Development Act of 1986 Public Law-99-662, the Energy and Water Appropriations Act of 1988 (San Timoteo), the WRDA 1990 (Santa Ana Trails), the WRDA 1996 (Prado Dam, State Route 71) and the WRDA 2007 (SARI Line).