GPS-based surface drifters were used to investigate the surface currents in Daya Bay and along the east Guangdong coast in China.Surface current vectors were measured based on the GPS location and corresponding time information sent by drifters through the mobile phone network.The analysis of data from 120 drifters,deployed in late spring 2018 in the case-study region,shows that the drifters are generally capable of capturing the surface (tidal and residual) currents.The drifter trajectories suggest an anticlockwise surface current inside Daya Bay and a north-eastward current along the east Guangdong coast,where the coastal current along the east Guangdong coast is faster than that inside Daya Bay.The surface currents in the investigated region follow an irregular semidial cycle due to the influence of the tidal current,while the currents inside Daya Bay are strongly affected by the topography.According to the harmonic analysis,an irregular semidial type of tidal current is evident at a study grid inside Daya Bay,with an Eulerian residual current speed of 9.0 /s and a direction of 276°.The Lagrangian residual current outside Daya Bay moves north-eastward with a mean speed of 22 cm/s along the east Guangdong coast,while the current inside Daya Bay moves northward to the bay head with a mean speed of about 8.0 cm/s,which agrees well with the one reported in other literatures.