This is just tip of the iceberg for that area. Georges Creek is another highly impacted stream which dumps into the North Branch in Westernport, a half mile above the waste water discharge. Depending on the flow, it mixes with the river at about the same point as the effluent. In low water, it's a bizarre greenish yellow and all the rocks in it's path are stained. But moving upriver there's another one or two streams with mine runoff that dump in above Bloomington with limestone buffers at the creek mouths. And there are apparently several above Randolph Jennings that are impacted as well. Here's a link about George's. It's an older article but still informative.
But back to the plant, and here's the kicker - the same paper company has an even bigger plant on the Jackson in Covington. Looking at that river above and below that Covington plant, you'd never think they were the same river. Below the plant, it's the same color and choked out bottom as the North Branch, for miles.
All things considered though, I'd say the North Branch is healthier than I would expect given the impacts from mountain top removal and abandoned subterranean mining, acid runoff, and the paper plant but still has a long way to go.