A participatory research team, concerned about water quality around Lake Geneva, particularly in the Montreux Bay region where some were lifeguards, ran sampling campaigns to determine summertime levels of lake water pollution. The participants were brought together serendipitously through a course organized by academic researchers and 'biohackers' from the community laboratory, Hackuarium. After discussion about lifeguards' gastrointestinal and dermatological ailments each season, the decision to pursue this participatory research project was made. In order to assess water quality, thereby testing the hypothesis that unsuspected pollution enters the lake each summer season, microbiological plating of water samples was proposed. Volunteers collected and analysed water samples over summer seasons (8 weeks in 2016, 2017 and 2020) from three sites around Montreux Bay, with tap and local river water samples as controls. Contamination of lake water was measured using standard microbiological methods, with growth media allowing quantitative assessment of abundance of several bacterial species. In particular, the focus was to quantify Escherichia coli, the classic bioindicator organism for raw sewage contamination. These open science data reveal peaks of bioindicator and other bacterial pollution in lake water samples during all sampling years. For the initial two sampling campaigns, increased microbial burdens occurred during a popular music festival, and were not simply dependent upon rainfall. In contrast, only scattered, lower level bioindicator pollution events occurred across the sampling period during the pandemic summer of 2020, when the festival was cancelled. This study confirms the power of participatory research: dedicated people on a budget can do meaningful environmental monitoring. These analyses suggest that better management, both to support water quality monitoring and for event organization, is essential, as sewage treatment facilities near many popular festivals, internationally, may need to cope with increased wastewater from visitors.