Hydropower has a well-established position in the energy sector, and it is very important to promote the further growth of this energy resource, especially in developing countries. As a result, the water flow modeling sector becomes a key area of study due to the importance of water resource management. Where, the precise forecasts of hydropower water flow are important for effective management practices. This paper provides a review on hydropower system. An overview on the method and techniques used to simulate water forecasting is made to provide further understanding. An analysis was also made to identify the techniques that provide high accuracy in hydropower flow forecasting.