This dataset contains average concentrations of water chemistry collected from stream catchments C31, C32, C33, C34, C35, C37, C38, C39, C42, C46, C47, C49, and C50 in the Turkey Lakes Watershed, approximately 60 km northwest of Sault Ste. Marie, Ontario, Canada. These are average concentrations recorded from 1981-2018 in milligrams per litre (mg/L) of major ions (Ca, Mg, K, Na, SO4, Cl, NO3-N, NH4-N) and some nutrients (TP, TN) collected by the Great Lakes Forestry Centre. Samples are collected according to variable schedules such that frequency generally increased with increasing stream flow, (sampling period was shortest during spring runoff, 1-3 days, and longest during winter, 2-3 weeks). Sampling was accomplished by rinsing an appropriately cleaned 2-litre, polyethylene bottle at least 3 times with stream water followed by immersion to collect the final sample. Care was taken to not disturb the stream sediments throughout the sampling procedure. pH and conductivity testing is completed right after sampling. Other chemical analyses are completed by the Great Lakes Forestry Centre in Sault Ste. Marie within 2 weeks of collection. Sample integrity was maintained through storage in the dark at 4 degrees Celsius and analyzed at room temperature.