In June 2019, the U.S. Geological Survey Maryland-Delaware-District of Columbia Water Science Center (MD-DE-DC WSC) team began to collect and inventory available information on toxic contaminants within the Chesapeake Bay Watershed. State agencies were contacted to determine available data. Also, the National Water Information System (NWIS) and National Water Quality Database (NWQD) were queried to gather relevant data for the compilation. The resulting tables contain records for available sites where specific analyte groups, Hg (mercury), PCB (polychlorinated biphenyls), or pesticides, have been collected with appropriate supplemental metadata including media, method, time frame, and frequency of collection. Sample results span 1972-2019. Files included in the data release: Basic_Table.csv Detailed_Table.csv NWIS_PCodes.csv State_Result_Totals.csv NWIS_Result_Totals.csv