GeoSurveyor
It is not natural. But, it is in process of being restored to wetland. Previously, it was a commercial salt pond. Then, recently the salt pond was acquired by government and became part of the South Bay Restoration projects. The levee was lowered, and more water has been allowed to flow into it. It is part of South Bay Salt Pond Restoration Project, Eden Landing Phase 2 Project. See the draft Environmental Impact Statement/Report from August 2017, figures 2-3 through 2-6. http://www.southbayrestoration.org/pdf_files/Eden%20Landing%20DEIS-R/2_Alternatives.pdf