Fehmarn Belt

Fehmarn Belt (), (, former spelling "Femer Bælt"; ) is a strait connecting the Bay of Kiel and the Bay of Mecklenburg in the western part of the Baltic Sea between the German island of Fehmarn and the Danish island of Lolland. Ferries operated by Scandlines connect Puttgarden and Rødby on the two islands.
The strait features an 18-kilometre (10 nmi) wide area with depths of 20–30 metres. Currents in the strait are weak and mostly dependent on wind.
Swimming.
It was initially swum across by Christof Wandratsch.
Tunnel proposal.
The Danish and German governments agreed on 29 June 2007 to build a fixed link to replace the ferry route. It is to save an hour on crossing the strait, and provide more crossing capacity.
In 2011, the Danish parliament voted overwhelmingly (with seven of eight parties supporting) for the €5.1 billion project that was intended to open in 2020. The tunnel is to have three separate bores, two containing two motorway lanes each, and one with a double-track railway line. Construction started on 1 January 2021.