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In the 1950s, the first large dams were constructed and today most rivers are “strongly fragmented” by dams and flow regulation. The most modified river is the Acheloos. The Evros, Axios, Pinios, Alfeios and Aoos are “moderately fragmented”, while only Sperchios and Evrotas are free-flowing. Over the past 40–45 years, the Balkan rivers have undergone marked discharge reduction, caused by climate variability and change, evaporation from reservoirs and extensive water abstraction for irrigation. For example, i the n Pinios basin, intensive use of water for agriculture deteriorated the water balance, which is strongly negative even in rainy years (Loukas et al., 2007) and resulted in lowering of the groundwater table by tens of meters (Marinos et al.,1997). In summer, river stretches in Pinios may dry out. Since the end of the 1990s, the water level of Lake Doirani has been receding as a result of drought and overexploitation for irrigation (Griffiths et al., 2002). Dam operation smoothes and modifies the hydrological regime downstream of reservoirs. Thus, Acheloos, Nestos and Aliakmon nowadays present high to maximum discharge in July due to peak hydropower production. In Acheloos, 30% of the annual flow occurs during summer (compared to 11% prior to dam construction). In several places  reservoirs retain vast masses of sediments thus adversely affecting delta evolution.