The Hamilton Wetland Restoration Project (HWRP) is a joint venture between the US Army Corps of Engineers (USACE; San Francisco District) and the California State Coastal Conservancy. The site is located on the property of the former Hamilton Army Airfield in Novato, California, along the western edge of San Pablo Bay, which is part of northern San Francisco Bay. The initial stages of wetland restoration, which included dredged sediment reuse, took place during 2009–2011. From 2011 until April 2014, the site was maintained as partially flooded through a temporary one-way culvert that allowed bay water onto the site. On April 25th, 2014, the outboard levee towards the north-eastern corner of the site was breached to restore tidal connectivity from the bay to the restoration area. The anticipated period for complete site restoration and marsh evolution is 10–15 years. During this period an active wetland vegetation replanting program was established by the USACE to augment the natural seeding by native plants. The various habitats on the restoration site include open-water sub-tidal, mudflats, emergent marsh, grassland, and upland transition zone. San Francisco Bay is contaminated with legacy mercury (Hg) from historic use in mining areas throughout the watershed, as well as from contemporary atmospheric and point-source inputs. Since wetlands are known to be particularly effective zones for the production of toxic methylmercury (MeHg) from inorganic Hg(II), the National Environmental Policy Act (NEPA) and California Environmental Quality Act (CEQA) documentation associated with the HWRP restoration identified MeHg production as a potentially significant impact of restoring the site to wetland habitat. As part of the USACE Monitoring and Adaptive Management plan (MAMP) for the restoration, the USACE was directed by the Regional Water Quality Control Board (RWQCB) and the San Francisco Bay Conservation and Development Commission (BCDC) to assess MeHg concentrations at the HWRP site. To fulfill this requirement, the USACE entered into an agreement with the U.S. Geological Survey (USGS) to conduct a multi-year and multi-phase investigation of mercury in biota (fish), water, and sediment at the HWRP site. The Sample and Analysis Plan (SAP) covers a period of 13 years and is divided into three phases. Phase 1 included the monitoring of sediment and water pre-breach [2013] and post-breach [2014], and the monitoring of fish pre-breach [2013 only]. Phase 2 covers the three-year period 2014-2016 (near-term post-breach). Phase 3 covers the nine-year period from 2017-2025 (long-term post-breach). Field sampling occurred once per year during a two-week window from mid to late June. A reference site, (Sonoma Baylands) managed by the U.S. Fish and Wildlife Service, was similarly sampled coincident with the HWRP site throughout the study. During the first year of study (2013, pre-breach), an additional reference site was sampled (China Camp) but was subsequently dropped. This data release summarizes the results to date for surface water and bed sediment. Fish data are not included. The list of surface water constituents include: filter-passing total mercury (THg) and methylmercury (MeHg); particulate THg, MeHg and divalent reactive mercury (RHg, operationally defined); particulate organic carbon (POC) along with the carbon-13 isotopic composition (δ 13C-POC); particulate nitrogen (PN) along with the nitrogen-15 isotopic composition (δ 15N-PN); total suspended solids (TSS); chlorophyll_a (Chl_a); specific conductance (SpC); dissolved oxygen (DO); pH; oxidation reduction potential (Eh); and temperature. The list of bed sediment constituents include: THg, MeHg, RHg, iron speciation [ferrous iron (Fe2+), crystalline and amorphous ferric iron (Fe3+)]; total reduced sulfur (TRS); Eh; organic content as percent loss on ignition (%LOI); grain size; porosity; wet bulk density; and temperature. This data release includes five data tables given both as Excel (.xlsx) and machine readable 'comma-separated values' format (.csv): 1) ‘T1-HAM-Data-Dictionary_v2.0’, the Data Dictionary, which provides definitions and details related to the other three data tables and includes analytical methods citations; 2) ‘T2-HAM-sed_v2.0’, the bed sediment analytical dataset; 3) ‘T3-HAM-water_v2.0’, the surface water analytical dataset; 4) ‘T4-HAM-WQ-Sonde’, water quality sonde dataset; 5) ‘T5-HAM-QA_v2.0’, quality assurance data summary for the sediment and water datasets. In addition, file ‘Sampling-Sites_v2.0.kmz’ provides the sampling locations in a machine-readable geospatial file format (*.kmz). Specific updates associated with version 2.0 of this data release are summarized in the file 'Hamilton_version_2.0_updates.txt.' First posted - July 07, 2020 (available from author) Revised - June 22, 2021 (version 2.0)