I'm flabbergasted that the game was allowed to ship with those painted on rivers. There must be a reasonable explanation for it. It's nothing to do with budget, can't possibly be due to the game being rushed out - it's a basic piece of design! I'm sure there will be mods out to sort the rivers out but it's ridiculous that there needs to be a mod for this in the first place.
For the record, playing on the highest possible settings with DX11.