Long-term freshwater quality monitoring data for sites in the Maritime Coastal basin for the past 15 years or longer for nutrients, metals, major ions, and other physical-chemical variables are included in this dataset. Monitoring is conducted by Environment and Climate Change Canada (ECCC) and Parks Canada as well as through the Canada-New Brunswick Water Quality Monitoring Agreement, the Canada-PEI Water Annex, and through collaborative work with the province of Nova Scotia to assess water quality status and long-term trends, detect emerging issues, establish water quality guidelines and track the effectiveness of remedial measures and regulatory decisions.