The Afsluitdijk is primarily a flood defense, but has various functions; from flood risk management, fresh water supply, ecology, traffic and transport by road and water to cultural history and recreation. To protect the area behind against flooding, the dike must be high and strong enough to withstand the sea in the most extreme conditions. The two lock complexes in the Afsluitdijk, the Stevinsluizen at Den Oever and the Lorentz locks at Kornwerderzand, discharge excess water to the Wadden Sea . That water comes from the IJssel , a branch of the Rhine that originates in Switzerland and the IJsselmeer.flows in. These locks are used by both professional and recreational vessels to get to and from the Wadden Sea and are very important because of the accessibility of the Northern, Central and Eastern Netherlands.

The IJsselmeer is an important freshwater reserves for the Netherlands. In dry periods, for example, water for agriculture can be channeled to the surrounding areas, the water is used as drinking water and it has ecological functions. It is important for many bird and fish species. The Afsluitdijk turned out to be an impregnable obstacle for fish migrating from fresh to salt water, and vice versa. That is why a fish passage has been constructed on the west side of the lock at Den Oever. In addition, a 4-kilometer long fish migration river will be constructed near Kornwerderzand, which crosses the Afsluitdijk. This river ensures that the Waddenzee and the IJsselmeer are connected again and that fish can easily swim back and forth.