The San Joaquin Marsh and Wildlife Sanctuary is a 300-acre coastal freshwater treatment wetland comprised of a series of pond and riverine systems located in Irvine, California. It was originally developed for the purpose of recreational duck hunting but was restored in the late 1990's to a more natural habitat with the intention of improving local water quality. The marsh effectively removes aquatic pollutants from the San Diego Creek via natural biogeochemical processes. This subsequently enhances habitat quality and biological diversity for the downstream ecologically sensitive marine habitat of the Upper Newport Bay. Routine monitoring of water quality, sediment composition, vegetation and wildlife has provided data and insight into best management practices for freshwater treatment wetlands in a region deplete of these crucial natural resources. The marsh has become a refuge for wildlife in an otherwise heavily urbanized southern California region and is home to over 200 bird species, some of which are species of special concern in California. 

As a pioneer of constructed treatment wetland technology in the region, the San Joaquin Marsh attracts various agencies and researchers who are interested in implementing this technology elsewhere. The Irvine Ranch Water District in partnership with Sea and Sage Audubon Society hosts academic programs to engage the community in natural history and ecological education. Over twelve miles of trails traverse habitats ranging from coastal sage scrub to shallow open water ponds to riparian forests, which attracts visitors for both recreation and scientific research. Currently, researchers from the University of California Irvine, Concordia University, Chapman University and various local high schools are utilizing this wetland system in order to understand the biogeochemical processes within coastal freshwater systems.