The Regional Ensemble Wave Prediction System (REWPS) uses the third generation spectral wave model WaveWatch III® (WW3) to arrive at probabilistic predictions of wave elements from the current day out to 3 days into the future. The probabilistic predictions are based on 20 ensemble members and a control member that are forced by the 10 meters winds from the Regional Ensemble Prediction System (REPS). An ice forecast from the Water Cycle Prediction System of the Great Lakes (WCPS) is used by the model to dampen or suppress wave growth in areas covered respectively with 25% to 75% and more than 75% ice. WW3 (WAVEWATCH III® Development Group, WW3DG 2019) is a third generation spectral wave prediction model that solves the evolution of the energy balance equation for the 2-D wave energy spectrum without any prior assumptions on the shape of the spectrum. The WW3 model has been implemented by a growing number of national operational forecasting centres over the last several years. The REWPS data are available on the Great Lakes domain.