Dick responded, "It looks like it has some sort of causeway running across it, but that will be a feature known as a glacial esker."
I showed him this photo I found online of Culbert Lake, and asked him, "Isn't it beautiful?" ...
... and with typical Culbert humour he replied, "It is taken far enough from shore that you don't see the clouds of black flies and mosquitoes endemic to the region."
UPDATE: Culbert Lake is named after Flying Officer Frederick Campbell Culbert (1910-1943) of Manitoba.