<p>Empirical research has extensively documented the psychotherapeutic value of various natural environments. However, the psychological health implications of water-based outdoor settings (aquatic ecosystems) remain inadequately conceptualized. And current scholarship predominantly documents physiological responses to marine environments, with limited theoretical frameworks explaining the complex psychological effects in water-based outdoor physical activities. 11 university students from the Xiamen University Diving Association participated in semi-structured interviews to share their experiences with water-based outdoor physical activities. The data were analyzed using inductive thematic analysis. Five experts unanimously validated the credibility and validity of the findings. This study extracted 8 themes and 21 sub themes: Fearful anticipation (fear, novelty seeking/desire for exploration); Safe-risking (safety needs, The impulse to take risks); Freedom with constraints (sense of freedom, sense of constraint); Solitude integration (enjoying solitude, team integration); Awe and confrontation with nature (awe for nature, confrontation with nature); Sense of meaning in life (belonging to nature, contemplation of ontological questions about life/world, self-efficacy); Sense of identity (professionalism, certification, risk management skills); Flow experience (temporal transformation, spatial transformation, action-awareness merging, task oriented, sense of control). This study suggests the distinctive psychological impacts of water-based outdoor physical activities on university students, offering insights for psychological interventions in physical education. It extends Maslow’s Hierarchy of Needs by proposing a nested, context-dependent structure. While the findings provide innovative perspectives on water-based outdoor settings’ influence on mental health, further research is necessary to confirm applicability across diverse contexts.</p>