Benzophenone-3 (2-hydroxy-4-methoxybenzophenone) is present in many sunscreens/cosmetics due to its UV-filtering properties and has consequently been observed in recreational waters. There are growing concerns about endocrine disruption in aquatic organisms and broader impacts in freshwater and marine systems. Therefore, there is value in cost-effective, sensitive techniques that allow for high-density, spatiotemporal data to protect environmental health and inform public policy. Condensed-phase membrane introduction mass spectrometry coupled with liquid electron ionization with in situ chemical ionization (CP-MIMS-LEI/CI) is a novel direct tandem MS technique that fulfills these criteria and was applied for the direct measurement of benzophenone-3 in environmental water samples without any sample preparation. We report results that are sensitive (20 ng/L detection limit), reproducible (11% interday variability), and comparable to those of liquid chromatography tandem mass spectrometry (LC–MS/MS) for environmental samples (n = 4; 12–24% different). CP-MIMS-LEI/CI was applied to samples (n = 33) from the Cowichan River and Cowichan Lake (British Columbia, Canada), an important fish-bearing system significant to First Nations culture, salmonid production, and recreation. The quantitative analysis afforded by CP-MIMS-LEI/CI enabled geospatial benzophenone-3 analysis, identifying elevated concentrations (>180 ng/L) associated with local recreational activity. LC–MS/MS measurements for samples from two locations suggest a correlation between the number of swimmers and benzophenone-3 concentrations (R 2 = 0.88 and 0.94).