My grandfather on the left, and friend making coffee,
My best guess is they were on Graveyard Island on Dinorwic lake. [Linked Image]
Note the Johnson Seahorse Ten, and Larson boat.
Graveyard island is so named because a missionary, Henry Johns, died at the age of 46, or so, and was buried on an Indian reserve.
It was mainland at that time, then the dam at Dryden raised the water level, and made an island of the spot.

These premises insured by a Sheltie in Training ,--- and Cooey.o
"May the Good Lord take a likin' to you"