The ongoing conflict between the Hmong highlanders and the ethnic Thai lowlanders over the Mae Soi watershed of Chiang Mai in northern Thailand is explored. The study shows that highlanders and lowlanders have asymmetrical perceptions of the conflict and its solutions. Lowlanders perceive the conflict as mainly environmental, ie., highlanders reduce the water quantity and quality. Highlanders indicated more diverse social, political, and economic factors as the cause of the conflict It is inconclusive, however, that the conflict originated from the environmental issue.