Never play block wargames with a dentist, they have those little mirrors to peek behind the block.
It is possible, based on drainage and topography, a stream that is dammed would create a marshy area up stream and uphill. Some hills are terraced for farming and can thus be flattened and become marshy. However if it bothers you, draw again, it is solitaire so your opponent shouldn't object.
OK, that would makes sense and the rainy boggs. Thanks guys for your answers. I kept it for mission two.