TELEMAC: an efficient hydrodynamics suite for massively parallel architectures. This paper investigates the use of TELEMAC (a Finite Element-based hydrodynamics suite) on massively parallel computer architectures. The performance of TELEMAC is illustrated using two separate test cases. The first considers the use of TELEMAC-2D for simulating tidal currents in the vicinity of a renewable energy marine turbine farm, in order to provide reliable estimates of the expected energy yield. The second demonstrates the use of TELEMAC-3D for assessing the effects of fresh water discharges on the salinity distribution in a coastal lagoon. The simulations have been performed with meshes ranging from 2 to 12 million elements, and good scaling performance is achieved on a variety of different computer architectures.