The electricity provider of the city of Zurich (ewz) has chosen Decision Trees GmbH (DTrees) as vendor of software for the optimization of its large-scale hydro power plants. DTrees will introduce the DT.Energy energy optimization system at ewz. DT.Energy is already widely used to optimize the operation and marketing of complex hydropower systems in the Alpine region. The first step is the deterministic long and medium-term optimization of eight power plant groups. Later in the project, the stochastic optimization of ewz hydropower systems will be delivered, taking into account uncertain long-term spot price and inflow evolutions. Finally, the short-term optimization of the entire hydropower system will be introduced.