Loch Moy, a beautiful calm gem. Not the deepest so not too cold. Swim out to the island and explore the ruins, and old tower.
Park at long layby on old road and walk back a short distance to enter loch. Or by old schoolhouse, making sure you are fully off the road and not hindering access to the house or gate in any way.
This is a crowd-sourced map. Abilities vary, and conditions change. Always assess risks for yourself before getting in.
Occasional branches and shallow areas near the rocky island.