The Hydrological Observatory of Athens (HOA) is operated by the Centre for Hydrology and Informatics (CHI) of the National Technical University of Athens (NTUA). It is located in the region of Attica, covering the greater Athens area and the Rafina basin. The region of Attica is characterized as a Mediterranean eco-region, which includes three main land use types: urban, peri-urban and rural. Forests are limited to the mountainous areas of Parnitha, Penteli and Ymittos, which are frequently threatened by devastating wildfires, affecting the local ecosystems, hydrology, soil erosion and climate conditions. The hydrographic network is fragmented, mainly consisting of small coastal basins and streams. The most important water body is river Kifisos, which is a heavily modified water body running through a heavily urbanized environment.