One of coastal Patagonia’s primo wildlife sites, the Ría Deseado submerges a long narrow valley that once carried more fresh water. As the freshwater flow diminished, seawater penetrated farther and farther inland, creating new islands and other fauna-rich habitats. Offshore islands also form part of the reserve.

Several operators organize wildlife-watching excursions in and around the Ría to locations such as the Magellanic penguin colony at Isla Chaffers and cliff-side colonies of rock cormorants and gray or red-legged cormorants at Banca Cormorán, where deep water permits close approach to the nests.

On any excursion, swiftly swimming toninas overas (Commerson’s dolphins) breach and dive around and under the outboard launches; in mating season, they leap out of the water.

At Isla de los Pingüinos, 30 kilometers offshore, there are breeding elephant seals, sea lions, and the world’s northernmost colonies of the tireless rockhopper penguin, which braves crashing waves up steep stone faces to reach its nesting sites. Some operators also follow Darwin’s route up the Ría where, wrote the great naturalist, “I do not think I ever saw a spot which appeared more secluded from the rest of the world, than this rocky crevice in the wild plain.”

In handsome new quarters that include a sea-view confitería, Darwin Expediciones (Avenida España s/n, tel. 0297/15-624-7554, www.darwin-expeditions.com) has extensive experience here, and also does sea kayaking. Half-day trips to Isla Chaffers cost about US$37 pp; full-day trips, following Darwin’s estuary route, cost about US$92 pp. A full-day excursion to the rockhopper colony at Isla de los Pingüinos runs about US$84 pp, with an eight-passenger minimum.

Turismo Aventura Los Vikingos (Estrada 1275, tel. 0297/487-0020 or, tel. 0297/15-6244283487-0020, www.losvikingos.com.ar) does similar maritime itineraries.