Study catchment areas (Greece). ALIAKMONAS Catchment (12410 km²⁾ is the largest river basin in Greece, characterized by mountainous and semi-mountainous areas. It includes the Aliakmonas river and Lake Kastoria. PINIOS Catchment (11062 km²) includes Pinios river and is characterized by the largest lowland area of the country. ACHELOOS Catchment (7530 km²) includes Achelloos river, Lake Trichonida (the largest natural lake in Greece), other numerous rivers, lakes and lagoons and remarkable mountainous regions. EVIA Catchment (3686 km²) includes the homonymous island (the second largest of the country) and displays diverse and complex geological structure with both mountains and lowland areas.