When the water is above about 800 cfs it's a class III (technical). The water can be as high as 20,000 cfs. At that point, it's a monster and I'd seriously think twice about running it. It's easily a class IV. The problem with millrace is that it's an old dam that was dynamited years back and is rumored to have rebar (steel rods that reinforced the concrete) all through the area.
Lines here are very much open to your discretion, not a whole lot of consequence and very easy to practice eddy hopping at normal levels. Anything center right all the way to river left is usally ok.
Millrace is often park and hucked, using the riverwalk on the river left side at the bottom of the rapid.
Rapid
Rapid
II
Rapid
I+
Playspot
II+
Playspot
III-
Playspot
II+
Rapid
N/A
Rapid
II