Flood Risk poses a serious threat for communities living near rivers. The scope of this work is to present the design and the stages of a web–based GIS (Geographic Information System) regarding the flood potential of the river Arachthos in the Epirus region. All the technologies and equipment installed are presented in detail. All the components of the system can be monitored by a web page making it available to the public. This system will serve as a trustful and accurate provider of information regarding real-time monitoring of the river flow and the early warning in cases of possible floods.