These data include benthic invertebrate occurrence data and associated water quality data within the states of Maryland, Pennsylvania, Vermont, and West Virginia. Data are sorted into stations dominated by chloride or sulfate ions or a mix of the two. Also included are the original and curated ion mixture data, R scripts, summary plots and tables. Additional detail on methods and applications are available in these two papers: Cormier, S., L. Zheng, and C. Flaherty. A field-based model of the relationship between extirpation of salt-intolerant benthic invertebrates and background conductivity. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, NETHERLANDS, 633: 1629-1636, (2018). Cormier, S.M., Suter, G.W., Fernandez, M.B. and Zheng, L., 2020. Adequacy of sample size for estimating a value from field observational data. Ecotoxicology and environmental safety, 203, p.110992. This dataset is associated with the following publication: Cormier, S., T. Newcomer Johnson, and C. Wharton. Freshwater Explorer 2.0 Data and mapping capabilities and assessment examples. Presented at OWOW Webinar, Webinar, CT, USA, 06/24/2025 - 06/24/2025.