Panajachel's public lakefront is not a beach in the tropical sense; it is a place to look, stroll, take photos, and watch boats move across the caldera. The reward is the view of the three volcanoes across the water, especially in the clearer morning hours.
Swimming is possible in places around the lake, but water quality near busy towns varies. Treat this more as a viewpoint and promenade than a swimming destination. Sunset is atmospheric, though clouds often hide the volcanoes by late afternoon.