Analyses of trajectories of drift cards, released over a 2‐year period April 1969‐Aprit 1971, and hydrological observations at nine stations all occupied in and near Tasman Bay within 19 hours on 4–5 March 1970, show variable surface flows, which are strongly influenced by wind. Water characteristics are altered by insolation and coastal run‐off. The exchange times for the water in Tasman Bay were calculated for differing wind speeds.