This dataset includes stream chemistry for the Bear Brook Watershed in Maine (BBWM). The BBWM consists of two watersheds, the reference East Bear (EB), receiving ambient deposition, and the treated West Bear (WB), which received experimental elevated N+S deposition for 27 years. Stream samples were collected as grab samples and event samples (e.g. during snowmelt and rain events) using ISCO™ automated samplers from both EB and WB streams. Stream chemistry was interpolated between collections to develop annual or monthly stream water fluxes.