I have a creek that runs through my place, and the fenceline goes up to the water on both sides (I think orginally there was a fence straight across the whole thing).
They cross it and play in it on this side, but they've never gone upstream in it to get the next quarter section, despite grazing right next to the fence on both sides of the creek. Good, wet summers it comes up to their bellies.
As long as it never freezes so you never have to worry about one falling through the ice, I don't see any problems.
I'm picture a very nice place you have.
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