The goal of this study was to develop a suite of inter-related water quality monitoring approaches capable of modeling and estimating the spatial and temporal gradients of particulate and dissolved total mercury (THg) concentration, and particulate and dissolved methyl mercury (MeHg), concentration, in surface waters across the Sacramento / San Joaquin River Delta (SSJRD). This suite of monitoring approaches included: a) data collection at fixed continuous monitoring stations (CMS) outfitted with in-situ sensors, b) spatial mapping using boat-mounted flow-through sensors, and c) satellite-based remote sensing. The focus of this specific child page is to document the temporal high-resolution (15 minute) in-situ sensor data collected at the four primary CMS locations. The four primary CMS locations chosen for this study included: a) a Sacramento R. dominated site in the northern portion of the Delta (Freeport, FPT, USGS Station_no. 11447650); b) a site in western portion of the central Delta, which is associated with the Cache Slough Complex and is seasonally influenced by the Yolo Bypass when it flows (Liberty Island, LIB, USGS Station_no. 11455315); c) a site in the southern reach of the central Delta where the Sacramento and San Joaquin Rivers have strong seasonal influences on water quality (Middle River, MDM, USGS Station_no. 11312676); and d) a site in the eastern central Delta where the Sacramento, Cosumnes, and Mokelumne rivers have strong seasonal influences on water quality (Little Potato Slough, LPS, USGS Station_no. 11336790). These four sites were used for monitoring of optical properties and hydrodynamics at high frequency (15 minute) intervals over the 2-year study period. Specifically, the data collected at each site includes tidal stage; velocity; nitrate measured via absorbance spectrometry (SUNA V2, Seabird Inc); and optical measurements of turbidity, chlorophyll-a fluorescence, and fluorescent dissolved organic matter, all measured via deployable multiparameter sonde (YSI EXO2, Yellow Springs, Inc). The time series data for all four CMS sites was downloaded for the 2-year period of record (July 1, 2019 through July 1, 2021) from the USGS National Water Information System (NWIS) website (https://waterdata.usgs.gov/nwis), and are presented here in a single machine-readable datafile (CMS_TimeSeries_Data.csv), which includes data for all of the parameters described above. In certain situations, specific sensors were not operational at a given site for a particular time period, and thus the associated water-quality data are not provided as part of the time series record in those instances. These high frequency temporal records provide the explanatory variables used to modeled THg and MeHg concentrations over time and at high temporal frequency throughout the SSJRD.

This Data Release serves as a repository for a set of time-series data used in Scientific Investigations Report 2018-5040. The data represent continuous measurements of specific conductance, water temperature, and/or water level (stage), recorded by a variety of types of data loggers during three multi-day interference tests conducted on the Virgin River at Pah Tempe Springs during November 2013, February 2014, and November 2014. The data presented are the raw data downloaded from the data loggers and are organized according to the date of the test and the type and name of the observation site. The Data Release contains 3 items: 1. An explanatory table, "PahTempe_table1.xlsx", which indicates which parameters were collected and on what instrument at each site during a given test 2. The data, "PahTempe_data.zip"; this zipped file contains the raw data logger files in comma-separated values (CSV) format, organized into folders according to the date of the interference pumping test 3. The metadata document, "PahTempe_metadata.xml" Because these data were collected during multi-day interference pumping tests, they do not represent natural hydrologic conditions in the river, springs, or shallow groundwater system. Users of this data are advised to refer to the larger work citation for proper use and interpretation of the data.

This Data Release serves as a repository for a set of time-series data used in Scientific Investigations Report 2018-5040. The data represent continuous measurements of specific conductance, water temperature, and/or water level (stage), recorded by a variety of types of data loggers during three multi-day interference tests conducted on the Virgin River at Pah Tempe Springs during November 2013, February 2014, and November 2014. The data presented are the raw data downloaded from the data loggers and are organized according to the date of the test and the type and name of the observation site. The Data Release contains 3 items: 1. An explanatory table, "PahTempe_table1.xlsx", which indicates which parameters were collected and on what instrument at each site during a given test 2. The data, "PahTempe_data.zip"; this zipped file contains the raw data logger files in comma-separated values (CSV) format, organized into folders according to the date of the interference pumping test 3. The metadata document, "PahTempe_metadata.xml" Because these data were collected during multi-day interference pumping tests, they do not represent natural hydrologic conditions in the river, springs, or shallow groundwater system. Users of this data are advised to refer to the larger work citation for proper use and interpretation of the data.

This file contains the locations at which water quality data was summarized in the 1998 report entitled: Baseline Water Quality Inventory, Castillo De San Marcos National Monument. The data and locations existed in the United States Environmental Protection Agency's Storage and Retrieval (STORET) water quality database management system when the report was published.

This file contains the locations at which water quality data was summarized in the 1998 report entitled: Baseline Water Quality Inventory, Salinas Pueblo Missions National Monument. The data and locations existed in the United States Environmental Protection Agency's Storage and Retrieval (STORET) water quality database management system when the report was published.

Discrete water quality monitoring data from the Sacramento-San Joaquin Bay-Delta collected by the Environmental Monitoring Program. Data is also accessible via the [Environmental Data Initiative](https://portal.edirepository.org/nis/mapbrowse?scope=edi&identifier=458&revision=10).

This file contains the locations at which water quality data was summarized in the 2000 report entitled: Baseline Water Quality Inventory, Coronado National Memorial. The data and locations existed in the United States Environmental Protection Agency's Storage and Retrieval (STORET) water quality database management system when the report was published.