Manakara Beach is long, palm-lined, and better for atmosphere than swimming. The Indian Ocean here is exposed, with surf and currents that can be dangerous, so treat the beach as a place to walk rather than a place to drift out beyond your depth.
At dawn and late afternoon it is lovely. Fishing activity, low light, and the sound of the surf give Manakara its edge-of-the-island feeling, especially after the confined heat of the train.