Lake Köyliönjärvi is located in the village of Köyliö in the municipality of Säkylä. It covers an area of 12 km² and has a catchment area of 125 km². The ecological state of Lake Köyliönjärvi is moderate due to significant eutrophication. Land use within the catchment area includes diverse agriculture and also peat production and forestry. The lakeside is densely populated by permanent and seasonal residents.
Lake Köyliönjärvi has been a subject to various studies and projects over the past decades. During these projects, various restoration methods and water management practices have been implemented within the lake and its catchment area. The project aims to compile current knowledge and experience and form a restoration plan, which defines priorities and needs for restoration of Lake Köyliönjärvi and suggests suitable practices for enhancing the ecological state of the lake. These measures will also aim to preserve conservation values of local Natura 2000 areas. In addition, the needs for further knowledge and research regarding the lake area will be considered.