How can I "blend" a mesh (static or animated) into the sky ?

Imagine a sky sphere that is basically sky and the ocean, and actual ocean mesh on the level. How can I make ocean mesh gradually blend into the sky sphere so that the scene looks seamless ? (sky sphere could be a a desert and sky, with patch of desert landscape mesh; same idea - make scene look seamless)

Thanks!

Dont quite understand but maybe set a scalar opacity value in the materials that you can change?

This is what I made using old engine and that’s what I want to achieve with UE4 (but not sure how):

ss2 sky to terrain - YouTube << what it looks like in-game

ss2 dev stream 11 - YouTube << this is how it was made

Does it make more sense now? Basically there is no transparency/translucency, no alpha testing, no fog of any kind. The terrain surface casts shadow / receives shadow. There is no performance loss at all (between non-blending terrain and bending terrain you see on video).