We estimated how much of the water flowing into lakes during snowmelt replaced the pre-snowmelt lake water. Our data show that, as lake depth increases, the amount of water mixed into lakes decreased, because vertical mixing is reduced as lake depth increases. Our data also show that the water mixing into lakes is not solely snow-sourced but is a mixture of snowmelt and soil water. These results are relevant for lake biogeochemistry given the unique properties of snowmelt runoff.