Here we provide GPS drifter data from the near-field region, Deep Cove, in Doubtful Sound, New Zealand. A controlled freshwater discharge is carried from alpine lakes (Manapouri and Te Anau) through the Manapouri hydroelectric power station and, via a constructed channel, into the head of Doubtful Sound, located on the southwest coast of New Zealand (45.3 S, 167 E). The freshwater tailrace is discharged into the head of the inner fjord, Deep Cove. Deep Cove is 3.6 km long and, flanked by steep topography, has a maximum depth of 126m that occurs within 50m of the shoreline. A 2-week field campaign was conducted in March 2016.

Lagrangian measurements of near-surface currents were made during six GPS drifter experiments. The plume discharge rate and wind speeds for each experiment are detailed below, and wind direction was consistently up-fjord due to the surrounding steep topography.

The drifters each had a cylindrical drogue of height 0.5 m and diameter 0.2 m, and were ballasted to measure the upper 0.5 m of the water column by a small spherical float. Wind slippage was minimal as the float had little exposure to wind above the surface water level. Each drifter was equipped with a GPS receiver (Columbia V-900 GPS data logger) which recorded every 1 second. The GPS devices have a position accuracy up to 1.5 m, depending on satellite coverage. The drifters were released approximately 10 m apart across the width of the tailrace discharge point and were recovered after $\sim 1$ hour. A total of 8 drifters were deployed in the first two experiments then, due to the loss of a GPS receiver, 7 drifters were deployed and retrieved in the subsequent four experiments