Potmarks in my render

Hi guys

Can you please tell me why I have these black potmarks left in the mud that can be seen when viewing the scene from above?

Blend file is here:

Thank you

I can’t tell, as the mud textures aren’t included.

Though the 300 megabytes of 4k castle brick textures did come in. That seems pretty heavy for what it is, but you know your scene better than I do.