The Bear Brook Watershed in Maine (BBWM) is a long-term, whole-watershed study examining the effects of experimentally elevated N and S deposition on a treated watershed, in comparison to the adjacent reference watershed. The study is in a northern New England, USA, forested ecosystem, and focuses on soil and stream hydrological and biogeochemical processes, and chemical responses of vegetation. Relative to the reference watershed, the treated ecosystem has migrated biogeochemically towards N saturation, and soil and stream acidification. Some of the responses to N amendments were not expected nor predicted by available models.