Water Edge - Strange things happen here

[Rickmc]

Hi Forum,

I´m sure I doing something wrong but I can't find a solution.
As you can see in the Picture, there is a dark Something were the water touches a solid object.
What the hack is that and how can I get rid of it?

I´m gonna attach a simple C4D file, may this helps faster than a big story of all my settings.

Thanx

Insel_Start_05.c4d.zip

[sirio76]

Lower the shadows bias to 0.001:

[Rickmc]

As I expected, just a simple adjustment.
Thank you