Volunteer retention and data quality are critical aspects of successful participatory science programs. Program staff dedicate substantial time and resources to volunteer recruitment and training. When a volunteer chooses to leave the program – especially soon after joining - that investment is lost along with the monitoring data that volunteer would have collected. Furthermore, because of the scrutiny of volunteer-collected data from managers and decision-makers, participatory science programs must take steps to ensure the quality of the data that volunteers collect. We run Michigan’s Cooperative Lakes Monitoring Program (CLMP), a statewide inland lake volunteer monitoring program with a 50-year history. We have learned that personal, one-on-one support of our volunteers significantly increases retention and data quality. In addition to offering in-person training and frequent personal contact with our volunteers through telephone and email, we added a “side-by-side” data collection component to the CLMP in the early 1990s. Program staff visit approximately 10% of enrolled lakes annually, joining volunteers on the water and collecting data alongside them. These visits allow us to compare the data collected by volunteers versus professionals, address any observed protocol deviations and volunteer questions, and build a personal relationship with individual volunteers. New volunteers are prioritized for these visits. With over 325 lakes enrolled in the program in 2024 alone, the side-by-side component represents a significant investment of staff time and travel; however, we conclude that the value of volunteer retention and improved data quality justifies the cost.