California State Water Resources Control Board (SWRCB) is developing nutrient water quality objectives for the States surface waters, using an approach known as the Nutrient Numeric Endpoint (NNE) framework. The NNE framework establishes a suite of numeric endpoints based on the ecological response of an aquatic waterbody to nutrient over-enrichment (eutrophication; e.g., dissolved oxygen, algal biomass). The SWRCB intends to use dissolved oxygen (DO) as an indicator in the NNE framework for estuaries. All seven coastal Regional Water Quality Control Boards (RWQCB) have existing basin plan objectives for DO concentrations intended to maintain satisfactory water quality in enclosed bays and estuaries. However, these objectives are not consistent across the individual RWQCBs and reflect outdated science. Thus, recent advances in scientific understanding of DO tolerance in estuarine and marine organisms, as well as new methods for setting protective limits, may provide the technical basis for improved and more consistent objectives to protect beneficial uses. The primary objective of this document is to evaluate the current scientific basis supporting derivation of DO objectives for estuaries and enclosed bays in California. Ideally, such objectives would be applicable to the approximately 400 estuaries found in California and address regional (i.e., north-south) differences among organisms present.