Río San Juan’s main attraction is Laguna Gri-Gri, at the northernmost end of Duarte, and it comes as a wonderful surprise, a magnificent mangrove reserve traversed by organized boat tours that you can arrange and board from a small quay at the road’s end (589-2277). The 2hr tours, which cost RD$1200 per person (for 3 to 6; thereafter, RD$200 per person) head out of the lagoon through the mangroves; go early in the morning if you want to catch more of the birdlife. The boat then enters nearby Cueva de la Golondrina (Swallow’s Cave) to admire the stalactites and stalagmites, before heading along the coast to Playa Caletón, where you get to swim. You can also arrange to go snorkelling or fishing for an extra sum. To see the lagoon’s birdlife on foot, walk east from the Hotel Bahía Blanca to the peninsular bird sanctuary that the tour skirts, which is at its most active just before dusk when hundreds of egrets return to roost. Alternatively take the dirt footpath to the left of the tours office.
Campo Tours is the lone tour operator in town, but you’ll find better-quality tours, and operators, down the road in Cabarete.