Mirror Lake is located within the Hubbard Brook Valley, NH and has been the subject of numerous continuous limnological investigations since the early 1960s. The long-term Mirror Lake record is part of the Hubbard Brook Watershed Ecosystem Record (HBWatER), which is a long-term record of weekly sampling of nine-gaged watersheds at Hubbard Brook and includes sampling of the Mirror Lake inlets, outlets and water column. This data set reports Mirror Lake water column chemistry beginning in 1967 and continuing through 2014. The collection and management of the long-term record was initiated in 1963 by Gene E. Likens, F. Herbert Bormann, Robert S. Pierce, and Noye M. Johnson. HBWatER is currently sustained by Tammy Wooster (Cary IES) and Jeff Merriam (USFS) and the datasets are curated and maintained by a team of researchers: Chris Solomon (Cary IES), Emma Rosi (Cary IES), Emily Bernhardt (Duke), Lindsey Rustad (USFS), John Campbell (USFS), Bill McDowell (UNH), Charley Driscoll (Syracuse U.), Mark Green (Case Western), and Scott Bailey (USFS). Current financial Support for HBWatER is provided by NSF LTREB # 1907683 and the USDA Forest Service Northern Research Station. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station.