Translation:They had discovered a woman in the lake.
I know this was already answered somewhere already, but I couldn't find it: Apparently the baltic sea translates to östersjön, but sjön itself translates to lake. I find it a little bit confusing and as a geographer I concider basins with a large conection to the oceans and a high salinity as a sea, whereas lakes are inland water bodies that mostly contain freshwater (with few exceptions). So is there any rule of thumb when to translate sjön as lake and when as sea?
sjö used to mean sea, so you still find it for both seas close to Sweden: the Balsic Sea
Östersjön and the North Sea
Nordsjön. While wouldn't want to change the name of your neighboring sea lightheartedly, both are by definition
Östersjön är ett hav.
You can also find the old usage of the word
sjö in some expressions:
sjöfart navigation / shipping / sea voyage / maritime shipping etc.
gå till sjöss go to sea
sjöfartsmuseum maritime museum
(There are also some lakes in Sweden with
hav in their names, but that doesn't change that while maybe feeling like a sea to the people living close to them, they still are geographically speaking
A similarly confusing usage of "der See" vs "die See" exists in German.