This indicator compares median half total flow dates for the past 20 years (1992-2011) with those of the preceding 20 year period (1972-1991). ‘Half total flow date’ refers to the day of the year when half of the total annual volume passes through a monitoring station on a stream. Twentyseven active Basin Boundary monitoring stations measuring unregulated flows were included in the calculation. Raw data were gathered from the Water Survey of Canada. Stream flow timing influences the ecological processes in each stream and the availability of water for human use. A trend to earlier half total flow generally suggests longer periods of low flows in the late summer and fall. In addition to impacts on human use, low flows can contribute to higher water temperatures with implications for species that require cold-water habitats.