We present a three dimensional fluid-structure coupling between SPH and 3D-DDA for modelling rock-fluid interactions. The Navier-Stokes equation is simulated using the SPH method and the motions of the blocks are tracked by a Lagrangian algorithm based on a newly developed, explicit, 3D-DDA formulation. The coupled model is employed to investigate the water entry of a sliding block and the resulting wave(s). The coupled SPH-DDA algorithm provides a promising computational tool to for modelling a variety of solid-fluid interaction problems in many potential applications in hydraulics, rock mass stability, and in coastal and offshore engineering.