Changes in the Canadian definitions of break-up and freeze-up

Canadian definitions of break-up and freeze-up are shown to have changed substantially on several occasions since 1957. This paper demonstrates that because of these changes, great care must be exercised in the tabulation and interpretation of dates of break-up and freeze-up. In part, these changes have been occasioned by historical concerns, so that scrupulous attention to definition is necessary if the Canadian record is to be used for scientific purposes.