A dive shop in Marina Vallarta, two streets from the whale statue, with boats leaving at nine and a fixed weekly rotation: Los Arcos and the southern sites — Majahuitas, Colomitos, Mismaloya — on Monday, Wednesday, Friday and Sunday; the Islas Marietas on Tuesday, Thursday and Saturday.
Los Arcos is a cluster of granite islets at the south end of Banderas Bay with arches worn through them at sea level and a wall dropping past forty metres on the outside. It is a national marine park and the shallow side is good snorkelling.
From December to early April they run humpback whale trips in the bay. Banderas Bay is a calving ground and the whales are often close inshore.