The impoundment and abstraction of water from running waters affect the aquatic and riparian ecosystem. It is therefore necessary to maintain an appropriate quantity and quality of water in running waters in order to preserve and improve the aquatic ecosystem, which may be ensured by ecologically acceptable flow (EAF). In Slovenia, a great diversity of running waters and biological diversity demand the determination of EAF for each individual section of the running water, for which the knowledge of structure and functioning of the aquatic ecosystem is indispensable.
On the basis of hydrological, hydraulic, morphological and ecological criteria, hydroecological and ecohydrological methods are applied for the environmental flow (EF) determination in Slovenia. The EF value must ensure the running water regime which preserves the aquatic and riparian ecosystem while at the same time permitting water abstraction where ecologically and economically justified. This paper presents the basic characteristics of EF determination and experiences in the determination of EF.