El Golfo Dulce (The Sweet Gulf): Marine Sanctuary and Home to Costa Rica’s Fjords

Cradled between the Osa Peninsula and the mainland of southern Costa Rica, the Golfo Dulce is one of only four tropical fjords in the world—and a place where ocean, rainforest, and mangrove intertwine in a breathtaking display of life. This deep, sheltered gulf is a haven for marine giants and coastal ecosystems alike, with waters that plunge to over 200 meters and support a rich array of biodiversity. What makes Golfo Dulce truly remarkable, however, is its ecological role as a critical birthing and nursery ground for migrating humpback whales, making it one of the most important whale nurseries in the Eastern Pacific.

From July to October, and again from December to March, humpback whales migrate thousands of miles from feeding grounds near Antarctica and California to these warm, protected waters to mate and give birth. Calves can often be seen alongside their mothers, surfacing gently in the calm gulf waters—a rare and intimate glimpse into the early life of these majestic creatures. In addition to humpbacks, pantropical spotted dolphins, bottlenose dolphins, and even the elusive false killer whale can be seen year-round. Whale sharks, the gentle giants of the sea, occasionally make appearances in the deeper sections of the gulf, along with hammerhead sharks and blacktip sharks, particularly near reef structures and river mouths.

Along the edges of the gulf, lush mangrove forests thrive—among the most intact and diverse in Central America. These tangled root systems not only protect the coastline from erosion but also serve as nurseries for fish, crustaceans, and bird species, while filtering the freshwater runoff that flows into the sea. The Piedras Blancas National Park and Golfo Dulce Forest Reserve help safeguard these critical buffer zones, where land meets sea and life abounds in a quiet, ceaseless rhythm.

The gulf’s unique topography—where nutrient-rich runoff from rainforest rivers meets the deep marine basin—creates a rich upwelling zone that supports plankton blooms and a complex food web. This convergence of terrestrial and marine ecosystems makes Golfo Dulce a vital biological corridor, connecting the Pacific Ocean to the heart of one of the most biologically intense places on Earth.

Whether kayaking through emerald mangrove tunnels, watching a pod of dolphins leap alongside your boat, or witnessing a newborn whale calf take its first breath, Golfo Dulce offers a front-row seat to nature’s most awe-inspiring phenomena.