This Dutch 2015 animation video is called Fish Migration River Afsluitdijk.
Translated from Dutch NOS TV:
The fish tunnel should prevent extinction of fish species
Fish from now on will be able to swim without problems from the Wadden Sea to the IJsselmeer. Rijkswaterstaat has opened a special fish passage in the Afsluitdijk near Den Oever in North Holland. Such a crossing is important because some fish need both fresh and salt water to survive and reproduce.
For years, locks, weirs and dams in the Afsluitdijk have blocked the way for fish from the Wadden Sea to swim to the IJsselmeer, or vice versa. Some species thereby are even threatened with extinction. Rijkswaterstaat felt they needed to address this type of barriers. …
[Ecologist] Van der Herk says: “In the IJsselmeer there are for example only 1 percent of the original number of eels. If eels do not swim to other waters, they just won’t reproduce. Then these fish will become extinct…”
Bypassing the blockages should improve the migration of fish. The special passage – a tube – was built for, eg, eel, smelt, salmon, river lamprey and stickleback. Experts think every year about 350 million migratory fish will use the passage in Den Oever.