Some type of double reflection on my water plane?

Hey guys, im rather new to UE4, and this small thing was bothering me kinda. I created a Shape_Plane, to create a Water surface and also the post process box in this Water, Area. But everytime when im kinda passing into it, this kind of reflection happens.

I checked if the PPB is causing it, with turning it into invisible, and it was still like this. Picture in the Attachments. Can someone mabye explain why its like that ^^’

My suspicious is, that its some type of weird shadow. But im not really sure and also not really knowledgeable enough to play around with settings to find out what causes it.