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It is common for freshwater lakes near or above a latitude of 45° north of the equator, like Opeongo Lake in Canada, to accumulate surface ice in winter. A study from 1980 to 2006 showed that, in general, the number of days per winter that such lakes have measurable amounts of surface ice is declining. However, a researcher claimed that some lakes have instead seen an increase in the duration of ice, citing as an example .