Mercury (Hg) is a well-known toxic element and environmental contaminant. The central valley of California has long been identified as a hotspot for Hg contamination due to the historic mining of Hg in the California coast range, and its use in the mining of gold in the Sierra Nevada, with these mountainous regions bordering the east and the west of the valley, respectively. While the whole central valley is world renowned as a major agricultural area, the northern portion, known as the Sacramento valley region, is dominated by commercial rice production. Since rice is grown in flooded fields, and since wetland soils are known to be particularly effective habitats for converting inorganic mercury into the more toxic methylmercury (MeHg) form, there is increased interest in the extent to which rice growing wetlands can produce MeHg and the extent to which MeHg produced in soils can be exported in drainage water or taken up into the edible the rice grain. The dataset includes a survey of six commercial rice growing fields in the Sacramento valley, with respect to total mercury (THg) and MeHg in shallow surface sediment, surface water, and rice grain. The sampling period extends over a full annual cycle, from September 2017 through October 2018, and includes primary hydrologic and field management periods (initial field flooding, growing season, field draining / harvest, and post-harvest / fallow). Surface sediment was sampled from the field centers, while surface water was sampled at water control inlets, field centers, and water control outlets. Rice grain was sampled immediately before harvest (September-October) in both 2017 and 2018. This data release includes five tables provided in machine readable (comma-separated values, *.csv) format: 1) ‘T1_SacValley_dictionary.csv’, the Data Dictionary, which provides definitions and details related to the other four data tables and includes citations of analytical methods; 2) ‘T2_SacValley_sed.csv’, data associated with surface sediment; 3) ‘T3_SacValley_water.csv’, data associated with surface water; 4) ‘T4_SacValley_rice.csv’, data associated with harvested rice grain; and 5) ‘T5_SacValley_QA.csv’, quality assurance data summary.