The southernmost bay in Texas, located near Port Isabel. The bay consists of approximately 3,500 surface acres, bounded on the south by the riparian edge of the Rio Grande, on the north by the Brownsville Ship Channel and associated spoil banks, and on the east by Brazos Island. Submergent vegetation is reported near the mouth of the bay, while emergent vegetation is found along the northwestern boundary and near the mouth of the bay. Extensive algal flats constitute a significant portion of the southern end of South Bay and are an essential part of the organic production and fertility of South Bay. The Bay supports 41 species of finfish and 9 different species of shellfish. The preserve supports the largest concentration of oysters in the Lower Laguna Madre. There is evidence of a higher tolerance for salinity and turbidity in the South Bay oysters.