Baie-des-Sables is the main developed beach and outdoor base on Lake Mégantic, south of town. It has a sandy beach, marina, walking trails, and rental options for getting onto the water.
It is not wilderness, and in summer it can feel like a family holiday park. That is also its advantage: if you want a swim, a paddle, or a low-effort lake afternoon, this is the easiest place to do it.