This data release collates stream water temperature observations across the Chesapeake Bay watershed from the USGS National Water Information System (NWIS), Water Quality Portal (WQP) and the USGS Aquarius (AQ) Time-Series database. Data retrieved from NWIS consists of aggregate (minimum, maximum and mean) daily values and continuous data from USGS monitoring stations. Values from the WQP contain discrete data from multiple agencies. The dataset compiled from AQ includes miscellaneous stream temperature observations collected during discharge measurements. This stream temperature data release was completed to support the USGS goal to make scientific data publicly usable, easily discoverable, and widely available. A subset of these data will be used and published in the future to assess the status and trends of key indicators of stream health in the Chesapeake Bay watershed.

The ecological implications of rising stream temperatures are a concern to resource managers throughout the Chesapeake Bay watershed. This dataset provides analysis results for the recent status and trends of water temperature for select streams within the Chesapeake Bay watershed. An existing data compilation effort (https://doi.org/10.5066/P92SHG66) was used to gather continuous and discrete temperature data for the status and trend analysis. The status of stream temperature was computed as the change in 2022 in degree Celsius above or below the mean temperature for the reference period (trend interval). Site level trends were developed using generalized additive modeling (GAMs) in the R package “mgcv” for 31 sites with an average of 346 daily value stream temperature measurements per site collected from contemporary periods (2013-2022, 2014-2022, 2013-2021, 2013-2020). Discrete data were evaluated with linear mixed-models (LMMs) to produce a population-level trend for stream temperature. Detailed data preparation information, analytical methods and results are presented and discussed in the associated Scientific Investigative Report (https://doi.org/10.3133/sir20255072).

Freshwater salinization is an emerging issue for freshwater environments in the Chesapeake Bay, USA region. Salinization is often described by measurements of specific conductance (SC). This data release contains specific conductance observations collected by multiple regional agencies for streams within the Chesapeake Bay Watershed. This inventory compiles and harmonizes data from the Water Quality Portal (WQP), which is a data repository developed by the National Water Quality Monitoring Council and supported by the U.S. Environmental Protection Agency and U.S. Geological Survey, and the U.S. Geological Survey National Water Information System (NWIS). Both discrete measures of SC, which are single measures taken on a particular time and day, and continuous measures of SC, which are repeated measures of SC taken at regular, short intervals, such as 15-minute or hourly intervals, were compiled for this data release. The discrete data were also processed to screen out non-relevant observations and harmonize units. The WQP uses "MonitoringLocationIdentifier" to identify each unique site and monitoring activities, and this term is used throughout the data release to differentiate among unique sites and monitoring activities as well. The data release includes four items: 1. ["Site_inventory_for_specific_conductance_measures.csv"]: This is a site inventory of all locations where SC data had been collected and compiled for the data release. This file includes information on the monitoring location (coordinates, state, and county), the organization responsible for the data collection, the type of data available (discrete, continuous, or both) and its unique monitoring location and activity. 2. ["Discrete_specific_conductance_results.txt"]: This file contains all discrete SC observations. Identifying information (coordinates, monitoring location name and identifier), along with the observation value, units, and multiple flagging columns which denoted whether any changes were made to the observation or units during the processing steps. Full details are included in the "readme_file_for_Ches_Bay_specific_conductance_inventory.pdf" file. 3. ["Continuous_specific_conductance_results.zip"]: This zipped folder contains 89 .csv files for all the continuous USGS SC data available in the Chesapeake Bay watershed. Each file name includes each unique MonitoringLocationIdentifier. 4. ["readme_file_for_Ches_Bay_specific_conductance_inventory.pdf"]: This document describes all the processing and harmonization steps to generate the site inventory and discrete SC dataset, and for downloading the high frequency SC datasets.

Freshwater salinization is an emerging issue for freshwater environments in the Chesapeake Bay, USA region. Salinization is often described by measurements of specific conductance (SC). This data release contains specific conductance observations collected by multiple regional agencies for streams within the Chesapeake Bay Watershed. This inventory compiles and harmonizes data from the Water Quality Portal (WQP), which is a data repository developed by the National Water Quality Monitoring Council and supported by the U.S. Environmental Protection Agency and U.S. Geological Survey, and the U.S. Geological Survey National Water Information System (NWIS). Both discrete measures of SC, which are single measures taken on a particular time and day, and continuous measures of SC, which are repeated measures of SC taken at regular, short intervals, such as 15-minute or hourly intervals, were compiled for this data release. The discrete data were also processed to screen out non-relevant observations and harmonize units. The WQP uses "MonitoringLocationIdentifier" to identify each unique site and monitoring activities, and this term is used throughout the data release to differentiate among unique sites and monitoring activities as well. The data release includes four items: 1. ["Site_inventory_for_specific_conductance_measures.csv"]: This is a site inventory of all locations where SC data had been collected and compiled for the data release. This file includes information on the monitoring location (coordinates, state, and county), the organization responsible for the data collection, the type of data available (discrete, continuous, or both) and its unique monitoring location and activity. 2. ["Discrete_specific_conductance_results.txt"]: This file contains all discrete SC observations. Identifying information (coordinates, monitoring location name and identifier), along with the observation value, units, and multiple flagging columns which denoted whether any changes were made to the observation or units during the processing steps. Full details are included in the "readme_file_for_Ches_Bay_specific_conductance_inventory.pdf" file. 3. ["Continuous_specific_conductance_results.zip"]: This zipped folder contains 89 .csv files for all the continuous USGS SC data available in the Chesapeake Bay watershed. Each file name includes each unique MonitoringLocationIdentifier. 4. ["readme_file_for_Ches_Bay_specific_conductance_inventory.pdf"]: This document describes all the processing and harmonization steps to generate the site inventory and discrete SC dataset, and for downloading the high frequency SC datasets.

This data release contains measured streamflow data from U.S. Geological Survey (USGS) streamgages and reported wastewater data from wastewater treatment plants (WWTP) discharge monitoring reports (DMRs) within the Potomac River watershed between October 1, 2021 and September 30, 2024. Mean monthly streamflow data was obtained from 117 USGS streamgages (Table1_Streamgages.csv). Average monthly reported wastewater discharge volumes to surface water were obtained from National Pollutant Discharge Elimination System (NPDES) permits using the United States Environmental Protection Agency’s (USEPA) Environment and Compliance History Online (ECHO) database to obtain DMRs from the Integrated Compliance Information System National Pollutant Discharge Elimination System (ICIS-NPDES). Quality assurance procedures that were used to avoid inclusion of inaccurate data that can be reported on DMRs (Table2_WWTP_DMRs.csv) are documented within the Process Step fields of the metadata. At each streamgage the average monthly accumulated wastewater percentage (ACCWW) was calculated by dividing the total amount of reported wastewater upstream of the streamgage by the measured amount of streamflow (Table3_Streamgage_ACCWW.csv) following similar methods described in Miller and others (2024) and Barber and others (2025). The ACCWW calculations were computed monthly at each streamgage using reported total wastewater discharge, municipal wastewater discharge, and municipal-plus-industrial per- and polyfluoroalkyl substances (PFAS) wastewater discharge which includes municipal wastewater in addition to wastewater from industrial WWTPs that are potential PFAS handling industry sectors defined by the USEPA (2023). The term ‘municipal’ is used here to represent NPDES-permitted facilities with the Standard Industrial Classification code 4952 (‘sewerage systems’) and 'industrial' refers to permitted facilities with Standard Industrial Classification codes other than 4952. Monthly predicted environmental concentrations and constituent loads (i.e. mass fluxes) of eight PFAS and 14 pesticides were estimated at each streamgage following methodology presented by Barber and others (2025) and Miller and others (2024). Monthly PFAS loads were computed by multiplying the discharge volumes from municipal and industrial WWTPs that are potential PFAS handling industry sectors by the median PFAS concentrations measured and reported in Barber and others (2025). Monthly pesticide loads were computed by multiplying the discharge volumes from municipal WWTPs by the median pesticide concentrations reported in Miller and others (2024). Wastewater effluent concentrations from Miller and others (2024) and Barber and others (2025) are provided in Table4_Parameters.csv. Monthly predicted constituent loads from wastewater were summed from WWTPs that discharged to every National Hydrography Dataset Version 2.1 (NHDPlus V2; USEPA, 2012) stream segment Common Identifier (COMID) upstream of each streamgage, not including the COMID where the streamgage was located, to calculate the predicted monthly load at each streamgage (Table5_Streamgage_Parameter_Predictions.csv). Predicted monthly concentrations from wastewater were calculated by dividing the predicted monthly load by measured monthly streamflow at each streamgage (Table5_Streamgage_Parameter_Predictions.csv).

As part of a larger study examining stream conditions and the effect of Best Management Practices in the Chesapeake Bay watershed, thirty small streams on the Delmarva Peninsula were instrumented and monitored for gage height (water level), water temperature, and air temperature using Onset HOBO sensors from March to September 2022. In addition, two discrete discharge measurements were made at baseflow at each site. This data release contains four .csv files with time-series for gage height, water temperature, and air temperature for all thirty monitoring locations and a table of discrete discharge measurements and associated field measurement metadata: Delmarva_2022_Continuous_Air_Temperature.csv Delmarva_2022_Continuous_Gage_Height.csv Delmarva_2022_Continuous_Water_Temperature.csv Delmarva_2022_Discharge_Measurements.csv

As part of a larger study examining stream conditions and the effect of Best Management Practices in the Chesapeake Bay watershed, thirty small streams on the Delmarva Peninsula were instrumented and monitored for gage height (water level), water temperature, and air temperature using Onset HOBO sensors from March to September 2022. In addition, two discrete discharge measurements were made at baseflow at each site. This data release contains four .csv files with time-series for gage height, water temperature, and air temperature for all thirty monitoring locations and a table of discrete discharge measurements and associated field measurement metadata: Delmarva_2022_Continuous_Air_Temperature.csv Delmarva_2022_Continuous_Gage_Height.csv Delmarva_2022_Continuous_Water_Temperature.csv Delmarva_2022_Discharge_Measurements.csv

This dataset provides estimates of annual and seasonal precipitation for selected Chesapeake Bay watersheds. Season 1 is November-February; season 2 is March-June; and season 3 is July-October.

This dataset consists of historical estimates and future projections of land use and climate data summarized within the 1:100,000 National Hydrography Dataset Version 2 (NHDPlusV2) framework for catchments and upstream accumulated watersheds. Historical land use data are for the year 2005 and future land use projections are for the years 2030, 2060, and 2090. The projections offer a unique combination of thematic detail (17 land-use and land-cover classes). Historical climate estimates are averaged over the time period 1980-1999 and future climate projections are averaged over 20-year periods centered around the years 2030, 2060, and 2090. Climate data include seasonal measures of average air temperature (℃) and total precipitation (mm). The data set also includes bioregions as defined within the Chesapeake basin-wide index of biotic integrity for stream macroinvertebrates (Chessie BIBI). The COMID field (analogous to FEATUREID) can be used to link these data to the NHDPlus data suite. These data were used to develop models forecasting future stream conditions within the Chesapeake Bay Watershed under an array of potential future land use and climate scenarios. Results from this work can be used by researchers and managers to identify areas most suitable for conservation, mitigation, or restoration efforts while considering the non-static nature of the environment.

The data were collected summer, 2016, 2017, and 2018. Continuous temperature loggers were deployed along the Pend Oreille River between Albeni Falls Dam and the Box Canyon Dam. Loggers were checked every 1-2 weeks throughout the summer.