San Matías Gulf

The San Matias Gulf is an inlet of the Atlantic Ocean off the coast of Patagonia, Argentina. It is bordered by the Río Negro Province to the north and west, and the Valdes Peninsula of the Chubut Province to the south. It is "one of the largest gulfs in the Patagonia region".

The gulf was the subject of scientific investigation for its unusually large sand waves and their movement.

The local fishing industry may be unsustainably harvesting the Purple clam (Amiantis purpurata), the Tehuelche scallop (Aequipecten tehuelchus), the Blue mussel (Mytilus edulis), and the Ribbed mussel (Aulacomya atra), as well as the Patagonian octopus (Octopus tehuelchus).

The 2003 commercial squid harvest broke the previous record set in 2001 by more than double at 5,535 tonnes (5,448 long tons; 6,101 short tons).

As of 2014, this gulf is the only location in the world where swimming-with whales is permitted for tourism, with Right Whales.