Surf therapy is a novel form of small-group, nature-based mental health intervention that has proliferated globally in recent years. Self-reported outcomes indicate that surf therapy can be effective for enhancing mental health and wellbeing, but there is little theoretical understanding into the causal mechanisms of effect and limited strength behind the existing evidence base. This study employed a qualitative approach to explore the personal experiences and observations of volunteer surf mentors’ working with UK-based surf therapy charity the Wave Project. Five surf mentors (3 males and 2 females; mean age = 34.4 years, SD = 7.4, range = 19) were interviewed, data collected that related to first-person experience was analyzed using Interpretative Phenomenological Analysis, and that related to third-person observations of client experience using Thematic Analysis. Participation in delivery was affectively impactful for mentors. Affective experience of surf mentors correlated with past research into client experiences. Experiences for both clients and mentors were heavily influenced by environmental and social factors, and these factors interacted. Mentors were found to be both influenced-by and integral-to several key mechanisms of therapeutic effect. Findings demonstrate the research value of the perspectives of surf therapy facilitators and provide guidance for future research and for general service optimization.