Question about worlds

is it possible to create two Worlds in one scene?
for example: one for the sky and one for the sea
i would appreciate your help

You can create many worlds. But if you do not click on the F button (stands for fake user) when you save the Blend file only the currently linked world will be saved. When the fake user flag is enabled (works for many data objects in Blender not just the world) Blender assumes the datablock is still in use and will save it with the BLEND file.

Only one world can be visible at one time.

Thanks for your reply Atom but my question really was if you can see multiple worlds at same time/scene, well i guess that isn’t possible.