This video is called Scotland’s Big 5 – Harbour Seal.
Translated from Staatsbosbeheer in the Netherlands:
Tuesday, October 6th, 2015
Probably the seal swam via the Haringvliet or the New Waterway into the nature reserve. Because there is plenty of fish in the Biesbosch, the animal will remain strong enough to swim back to sea under its own power.
It remains a rarity to see these animals in the Biesbosch. … The last two observations were in March 2002 and in December 2012.