in 1940, 13 transport planes took off from Berlin, 11 landed on the frozen lake Hartvikvatnet, and never left. The lake melted in spring, they sank, some have been salvaged, a couple are still in the lake (Thanks Asterix!)

Like I said, some are still there. 

The 13 planes flew to Norway in a World War II mission to transport troops out, or bring supplies in to supply Germany troops at an important shipping port, as the supplies by German ships had been stopped by the allied ships

The winter mission was very risky and behind enemy lines, and did not succeed when the aircraft were damaged when landing on the frozen surface of the lake, making them unable to take-off again.

When the ice melted in the spring, the aircraft sank to the lakebed, where they remained for more than 40 years.

and some have been lifted out

The Militärhistorisches Museum der Bundeswehr - Flugplatz Berlin Gatow has assisted in several recoveries of underwater

A Ju 52/3m airplane recovered from Lake Hartvikvann near Narvik (Norway) in a joint project by Gunther Leonhardt (Aviation Museum Laatzen-Hannover), on 22 August 1986. Today, the plane is on display in the Ju 52 hangar of the Wunstorf airfield on loan from our Museum.

A Focke-Wulf 190 D-9 plane recovered from Lake Schwerin in Nov 1990.

Parts of the Fritz X guidable rocket bomb recovered in Hesedorf in June 2008.

 A Messerschmitt Bf 108 Taifun plane recovered from the Jasmund Bodden on the island of Rügen in Nov 2009

 A Junkers JU 88, recuperated from the Baltic Sea close to Sassnitz in June 2012, by the museum, divers from Mountain Engineer Battalion 8, Ingolstadt and the crew of German Navy seagoing tug Spiekeroog. The wreck is now being preserved in the museum conservation center and examined by museum historians.

https://ktsorens.tihlde.org/flyvrak/hartvigvann.html
https://www.ju52-halle.de/de/exponate/junkers-ju52/bergung
https://www.facebook.com/MHMGatow
http://mhm-gatow.de/en/recoveries