Vöyri River runs through a fertile valley in Vöyri, western Finland. It is an important agricultural area that has also been historically been called “the Kingdom of Rye” (original in Swedish: “rågens rike”). The river is about 35 km long and discharges into the shallow coastal brackish waters in the Baltic Sea. The catchment area encompasses 223 km² land and consists of mainly forests, agricultural lands, and bogs.

Large parts of the area has soils with underlying old marine sediments, containing iron sulfides. When these soils are ditched and the groundwater-level is lowered, these underlying sediments come into contact with oxygen. Iron sulfides react with oxygen to form acid sulfate soils. This can lead to high amounts of acidity in nearby rivers and streams, and also release soluble metals from the soils into the waters. These waters discharge into the brackish Baltic Sea. Thus, the discharge from acid sulfate soils can affect both the river itself, as well as the coastal environment. Vöyri River shows the close connection between the areas geological history, land use, and the watersystem. With smart water management the goal is to both improve the growing conditions and reduce the negative impacts of acid sulfate soils at the same time.