Background Aquatic warbler (Acrocephalus paludicola) is the rarest passerine bird species found in mainland Europe. With a very small world population, of around only 12 000 to 20 500 pairs, it is classified as vulnerable on the Red List of Endangered Species. The aquatic warbler depends on habitats such as fen mires and wet meadows, and is extremely susceptible to changes in land use. Once widespread and numerous, this habitat specialist has disappeared from most of its former range in northern Germany and Poland. The genetically-distinct population along the German-Polish border is now acutely threatened and the core population in north-eastern Poland has been restricted to very few sites. The aquatic warbler is listed in Annex I of the Birds Directive, and is a priority species for European Community funding under the LIFE programme. Most range states, including Poland and Germany, have signed an international Memorandum of Understanding for the aquatic warbler, which commits them to implementing an International Action Plan (IAP) for this species and its habitat. Objectives The LIFE project's main objective was to stabilise the population of aquatic warbler (Acrocephalus paludicola), in the species’ most important sites in the Biebrza region of north-eastern Poland and in Pomerania, Germany, through habitat management. The project also aimed to raise the awareness of authorities, key stakeholders and the public to the conservation needs of the aquatic warbler and its specific habitat requirements. To this end, it planned to identify and agree upon long-term management measures and to secure financial and political backing for their implementation. The project aimed to create 1 500 ha of new potential habitat in the Biebrza and Pomerania regions, and to implement restoration actions on another 1 500 ha. Measures to be implemented included hydrological management, removal of shrubs and overgrowth from wet meadows and mires, initiation of extensive grazing and considerate mowing of aquatic warbler habitats. Results The Aquatic Warbler project achieved its objective of stabilising the population of aquatic warbler (Acrocephalus paludicola) in key areas of its range in Poland and Germany, by simultaneously improving and increasing the habitat at the main EU stronghold of the species in the Biebrza Valley (Poland) and preventing the extinction of the genetically-distinct remnant population in Pomerania (Germany). The project area encompassed the breeding sites of around 81% of the remaining Polish and German populations and contributed to the implementation of the IAP for this species. The results of a monitoring programme at all nine project sites showed that aquatic warblers responded positively to management on degraded habitat. In the core project management area in the Biebrza Valley, 336 ha of restored habitat was re-occupied by the species, and in the time period from 2005 to 2010 the population of aquatic warblers increased by 20% in areas subject to active management. As a result of the project, 983 ha of land important for aquatic warbler conservation was purchased and legally allocated for nature conservation purposes. 971 ha of aquatic warbler habitat was restored by removing trees and bushes (314 ha of this being LIFE project funded). Another 6 166 ha was managed by regular mowing, partly using LIFE project funds, using specially-built machinery that is able to mow large expanses of fen mires without destroying the delicate peat soil (an effect like traditional hand scything). Grazing was successfully introduced on a further 510 ha, and proved an effective aquatic warbler habitat management tool. New agri-environmental schemes were prepared, which have been enforced since 2009 and widely promoted among farmers. These reward farmers who utilise aquatic warbler friendly land management measures, which should ensure the long-term legacy of the LIFE project. Water level management structures have been established in the project site at Karsiborska Kepa, which enables the regulation of water level to guarantee optimal habitat conditions for aquatic warblers. In the Peene Valley in Germany, the blocking of three ditches had a positive effect on 120 ha of potential aquatic warbler breeding habitat. The project investigated the possibility of using the hay cut from aquatic warbler sites for the production of carbon-neutral fuels and energy. Feasibility studies on alternative uses of biomass for Poland and the Lower Peene Valley in Germany were prepared. National Action Plans for the conservation of aquatic warbler in Poland and Germany were produced, which provide the basis for habitat management and help implement the IAP for this species. The Aquatic Warbler project successfully disseminated its findings through technical and layman’s reports, a film and a website. Project-related educational and promotional activities included around 124 events with over 41 000 participants. Public awareness-raising infrastructure established in different project sites included four observation towers, two hides, and a 400 m long boardwalk with an observing platform in Biebrza National Park; the latter has proved extremely popular among birdwatchers and is generally regarded as the world’s best place to observe aquatic warblers. In May 2016, five years after the project closed, the NEEMO external monitoring team conducted an ex-post follow-up visit. This confirmed that ongoing funding for regular aquatic warbler habitat management had been ensured through EU Rural Development agri-environment schemes and land lease schemes facilitated by the project for the years 2014-2020, including on the land purchased during the project. The project has contributed to improving the conservation situation of the target Natura 2000 network sites, the target species and the targeted habitat type. The bird’s population status has improved in Poland, and the population is starting to increase in the eastern locations; in particular, the number of aquatic warbler increased by over 20%, on average, in the Biebrza region between 2011 and 2015. However, it was considered that two major threats to the aquatic warbler population, identified during the project, still remain. Firstly, the weakness of the Pomeranian population means that habitat plots restored during the project and managed post-LIFE are still not occupied by the target species, though the possibility of re-introducing juveniles in these areas is being considered by the Aquatic Warbler Conservation Team (AWT) created by BirdLife International. The second main threat is habitat destruction and the deteriorating conditions of wintering grounds in Africa, which is starting to be addressed through cooperation between managers of protected areas in Senegal and AWT. The infrastructure built or refurbished by the project (observation towers, hides and boardwalks) is still in a good state and used by tourists. The project’s actions have also benefitted other species, in particular wading birds like redshank, lapwing and black-tailed godwit, whose populations have increased at most of the project sites. The Aquatic Warbler project was selected as a Best Life Nature Project 2013. Its feasibility study for using mown grass to make biomass pellets has been taken forward by the Biomass Use for Aquatic Warbler project (LIFE09 NAT/PL/000260), which is also coordinated by OTOP. Further information on the project can be found in the project's layman report (see "Read more" section).