Background The river Liesing in Vienna has been heavily modified as a result of flood protection measures, its use as a watercourse for a water treatment plant and by an increased riverside population. The “LiRiLi” project covering 5.5 km of the river will be part of a large–scale restoration project for the entire river Liesing. It will be the first river of this size to be restored in an urban area. The River Engineering department is experienced in this field as a similar project was implemented on the River Wien. Objectives The objective of the pilot project is to maximise the “ecological potential” of the River Liesing, in conformity with the Water Framework Directive and specifically with regard to “heavily modified water bodies”. A canal-like concrete channel over 5.5km in length and located in an urban area will be re-designed into a semi-natural river meeting the relevant flood protection requirements. The “LiRiLi” project also aims at an improvement of the water quality (from quality class IV to quality classII of the saprobic system) by restoring the river continuity and different flow conditions. The flora and fauna will be improved and high quality public recreational areas will be established. Finally, information on the project will be disseminated on a large scale. Results The revitalisation activities included construction measures to restore the river continuity, the restoration of semi-natural morphological conditions and former meanders, the construction of a semi-natural river bed with a gravel substrate, and the restoration of the river’s natural transport capacity. The steep banks were flattened and partly enlarged and are now protected by bioengineering measures (willow fascines, wattle fence). Existing mesoxerophytic grassland has been preserved by storing it during the construction work and replanting it afterwards. For landscape design only indigenous trees and bushes were used. A pathway and a riverside child's playground were also constructed. The project was accompanied by intensive PR activities. The project has resulted in the creation of aquatic ecological corridor through the urban area with new habitats for priority species and recreation facilities. A new sewer system was also created and a local treatment plant and morphological parameter that discharge the water to the river Liesing were closed. As a result, within a year the water quality improved from quality class IV to quality class II to III of the saprobic system.