This is the story of a dude, who piped a river and filled a whole pool

It's an island, you'll need a boat, standard boating safety rules apply.

The island has a couple of nice landings and there's little in the way of risks or hazards beyond common sense.

This article goes into much more depth than I can:

https://www.timminstoday.com/column/back-roads-bill/back-roads-bill-diving-deep-into-an-old-pool-9014162

Short version is that in the 50s a man built this concrete pool and a small cabin on this island, hauling all the materials himself, and even set up a system to pipe water from a smaller, higher spring fed lake to the east, running pipes all the way to the island.

The story goes that his wife did not like swimming in the lake.

Apparently after the man's death the little cabin was demolished and pushed into the pool and burned.