This 2015 video is called Brown Trout (Salmo trutta) Underwater UK.
Another video used to say about itself:
Translated from the Dutch Wadden Sea Society:
Sea trout will be freed in Lauwersmeer
On Friday, March 6th 1000 sea trout will be released into the Lauwersmeer lake. It’s the start of a multi-year restoration of this iconic migratory fish. A large coalition of nature lovers, anglers and regional governments want to work to let the trout swim again in healthy numbers between the Wadden Sea and their spawning grounds in Groningen and Drenthe. For the multiannual program this month a request for contributing financially by the Wadden Fund has been submitted.
Thanks to one-time contributions from the provinces of Groningen and Friesland, in anticipation of the implementation of the multiannual program, now sea trout will be released already into the Lauwersmeer.