The Water Cycle Prediction System (WCPS) is a forecasting system operated by Environment and Climate Change Canada since 2019. It aims to simulate the water cycle of regions where large lakes and coastal oceans have a significant influence on the water cycle. Every 6 minutes, the GEM atmospheric model communicates to the NEMO-CICE ocean-ice model the state of the atmosphere over water. In turns, NEMO-CICE informs GEM of the water temperature, the ice cover, and the turbulent fluxes. GEM also provides surface runoff to the WATROUTE river routing model. In turn, WATROUTE informs NEMO of the river flow into each lake modelled by NEMO. Each component can operate on its own grid and resolution (currently 10 km for GEM and 1 km for NEMO-CICE and WATROUTE). Initially implemented over the Great Lakes and St. Lawrence River watershed in support of Canada's obligations under the Boundary Waters Treaty as well as search and rescue operations, the domain was extended to also cover the Gulf of St. Lawrence region in 2021. 84h forecasts are provided four times per day. A system upgrade from v3.0 to v3.3 should be implemented during the summer of 2024. It will include and extension of the river routing domain to the Bay of Fundy. An assessment of the impact of this upgrade is presented, followed by an evaluation of the contribution of WCPS to a multi-model prediction of Great Lakes net basin supply. Finally, options for further developing and improving WCPS in the future are discussed.