Trends in the dates of river freeze-up, river ice break-up, and periods of ice-cover. Upward pointing triangle indicates a delay to the beginning of the freeze-up or break-up periods; or to the lengthening of the ice-cover period. Downward triangle indicates an earlier occurrence to the start of the freeze-up or break-up periods; or to the shortening of the ice-cover period. Trends significant at the 1% and 10% levels are marked by larger filled and hollow triangles, respectively. Smaller triangles indicate that trends are not significant at the 10% level. Source: Zhang, X., K.D. Harvey, W.D. Hogg, and T.R. Yuzyk, 2001: Trends in Canadian streamflow, Water Resources Research, 37, 987-998.