It's the same problem as described here -
http://forums.civfanatics.com/showthread.php?t=504799 Screenshots are included. It's like that on all maps, not just Communitas.
I have a Geforce GTX 750ti and I have the same problem on both DX9 and 11.
Found out that this only happens on random maps with the Anno Domini mod. Without mods or on constant maps, marshes look like they should.