I grew up in Phillipsburg, NJ and have been fishing the LV streams since 1966. The picture is complicated, but in general there seems to be a decline. Back in the 60's people said the limestoners were immune to urbanization, but now I think resistant is a better word. On the plus side, the Saucon was a dead stream from the zinc mine waste until the 1980's.
Back in the 60's all the limestoners had luxuriant weed beds, just filled with scuds. One could run your hands through the weeds and get a handful a scuds. The weeds kept the trout fed all year, but made some spots tough to fish. The pool above the dam at Binney and Smith was all weeds and it had wonderful hatches of olives and tricos with what seemed to be constantly rising fish. One couldn't use any underwater tactics with all the weeds, but the dry fly fishing was consistent. Actually, back in the day I preferred to fish the pool above than the plunge pools and riffle below.
First sign of stream degradation is that nearly all the weed beds disappeared by the mid 80s, but fishing was good and the Saucon was an emerging hot spot before the word got around much. Most places siltation was making the bottom unstable, but the Bushkill also had the very fine silt coming from the cement mills in Nazareth. In the Bushkill, they knocked down all the old stone arch bridges and put in modern steel bridges, usually straightening the stream in the vicinity of the bridge. This didn't help things IMHO.
In late 90's and early 2000's I was addicted to trico fishing and commonly went to work late to hit the hatch on the Bushkill, Saucon, or LL. Fishing pressure hurt this fishing. One morning I was fishing the Saucon early for the female duns and got a few, then I waited for the main event. That day the spinner fall was great, but there were no risers. Over on the Bushkill, catching one fish in a pool put all the fish down, something I never saw. On the other hand, the Heritage Stretch always saw the effects of pressure. The fishing was great the first two weeks the tricos were on, but the crowds got the fish spooky and other places fished better. In general, I would avoid the Special Regulation areas for better trico fishing.
I fished the LL every Sunday afternoon in the winter in the late 90's with some buddies. I typically caught about 20 fish in 3 hours or so of fishing and it was nearly all sight fishing. Most were nymphing, but there were plentiful hatches of brown, olive, and cream midges and plenty of olives on dull days. It was a great place to teach flyfishing because one could see the feeding fish, how the fly drifted to the fish and the fish's reaction.
The flood/drought yo-yo we have been on since the late 90's hasn't helped. For 30 years I never remembered the LL Fly Shop getting flooded, then all of a sudden it seemed to flood every other year.
I would say siltation is a major culprit for the decline. Of course the shallower streams push all the trout to the margins which makes fishing harder. I also think wading in the Heritage Stretch moves the fish around and makes them spookier.
The LV limestoners are still a decent place to fish, but don't have the steady fishing of 15 to 20 years ago in my opinion.
