Once the Wisconsin Ice Sheet fully melted, the basic dimensions of the lake were fixed. However, the rocks we see today needed to rebound by about 170 m from the weight of the glacier ice. The last ice age gives Blackstone a surface area of about 5.2 km², a volume of 0.1 km³, a mean depth of just over 20 m, a perimeter of nearly 35 km.
As the world 's climate entered a warm inter-glacial period, about 7000 years ago with Blackstone 's region being about 1°-2° C above the 20th century norm. With this climate shift the lake was again inundated with water during the Nipissing Phase. However, by 3500 ago the lake would have begun to be familiar in terms of lake levels, views and the types of trees initially being mainly White Pine followed by Oak and Birch.
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For the last 5000 years Blackstone Lake and surrounding area has had a stable climate with its current climate of a mean July temperature of 18°C and a mean January day temperature of -7°C. Unlike the summer, the winter is strongly moderated by Georgian Bay. The expected number of frost-free days is 140. As the lake is in a snow belt caused by the lake end effect, it receives at least 2.5 m of snow. The lake effect also contributes to the total annual precipitation of 100 cm. This climate and the shield itself allows for a Boreal ecozone with podzolic soil. The dominant trees are now Pine, Birch and Maple.
Blackstone Lakes water is soft in comparison with the Great Lakes hard water. For comparison, Lake Ontario has over 200 ppm of dissolved solids whereas Blackstone has a value, measured in July 1969 by The Ministry of Natural Resources as 23 ppm. This low amount of dissolved solids makes the lake 's water, void of any other consideration, an ideal drinking