The control sluice, also known as the "4T műtárgy", was built as part of the first phase of the Kis-Balaton water protection system in 1986. Its main task is to clean the water of the Zala River and keep dissolved nutrients out of Lake Balaton. A larger and a smaller sluice also regulate the water level of the Zala River and the Kis-Balaton before the waters reach Lake Balaton. The stone basins on both sides of the sluice form a fish ladder that allows fishes to pass from the Zala River into Lake Hídvégi, even upstream, as the sluice is not passable for fishes.