This prospective, longitudinal randomized controlled trial will enroll up to 86 active duty service members with major depressive disorder who are seeking surf or hike therapy as part of their standard medical care. Participants will be randomly assigned to receive 6 weeks of either surf or hike therapy. Assessor-administered and self-report measures will be completed at pre- and post-program, as well as three months following program completion. Participants also will complete brief, self-report assessments before and after each program activity session.