That's by the Hospital Road bridge, right? I glimpsed those signs myself. The land on the east side of the river MAY be owned by the Water Supply Authority. I know for a fact, however, that the land on the other side of the river is public.
Just do what I do: keep fishing until someone kicks you off.
Edit: Yep, sign says "Water Supply Authority" on the bottom.
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Now the sun is just starting to climb up over the treetops,
And it's gonna be a beautiful day, that's plain to see.
But I won't be around at all, so don't even bother to call,
Cause on a day like today there's one place I gotta be:
GONE FISHIN'
Fishing with LardAlmighty on YouTube