The Puyuhuapi fjord has previously been reported as one of the hypoxic fjords in Patagonia (dissolved oxygen -DO below 2 mL L-1). Hydrographic sampling between 1995-2015 confirmed hypoxia below 100 m depth, down to the bottom (250 m). A line of sensors at an oceanographic mooring in Puyuhuapi were deployed to continuously record the temporal-vertical behaviour of water column temperature and salinity from the surface down to ~120 m, from February to July 2015. A multi-Parameter water quality sonde was deployed at the bottom of the line, with a DO optical sensor. From February to mid-May, hypoxia was sustained (1.4-1.6 mL L-1). However, from May until the end of June, DO values increased (2.8 mL L-1), exceeding the hypoxia threshold. This was the first event of deep ventilation reported in a Patagonia fjord. During this time period, deep water temperatures increased by ~1.3 °C, coinciding with the decreased in salinity from 33.6 to 32.8. The main cause of this event was attributed to the arrival of a new volume of mixed oceanic water into the fjord, transported by Modified Subantartic Water, with warm temperatures and slightly higher DO values, given its origin in the surface layer of the outer region of the Patagonian fjords and channels.