I went out this past weekend with a few of my friends, who are all a bit more outdoorsy than I, and a few of the fisherman in the group were complaining about the Delaware and the surrounding tributaries. It hasn't really been covered by the "major" news outlets up here, but after talking with them, and doing some research I found out a bit more.
Didymosphenia geminate, or "rock snot" as is had been nicknamed, is an invasive freshwater diatom (microscopic alga). Didymo can form extensive “blooms” on the bottoms of rocky river beds, essentially smothering aquatic life forms such as macroinvertebrates (aquatic insects), native algae, and other organisms. Didymo uses stalks to attach to rocks and plants in a river system. The diatom actually creates these stalks, which can form masses 3 inches to 5 inches thick on the river bottom, and trail for lengths of 2 feet to 3 feet in the current. It is actually the stalks that are more problematic than the alga. The alga will eventually die off and decompose, while these stalks tend to persist for several months on the river bottom.
It is not native to NY. It started showing up around 2006-07, and has been getting steadily worse. I guess no one is sure exactly where it is originally native too, although it has been in New Zealand for decades. It can easily stick to waders, boat and canoes, even fishing lures. Only a few of these alga need to be transferred to start a new colony.
The problem is the invasivness, it kills all the small insects that the fish feed on, so it is a real threat to the river and stream's fish population. Apparently there has already been documented declines. And a large part of our tourism depends on the weekend, and vacation angler. I went and checked it out myself in Hankins. For a lack of a better term, its gross.
From what I can gather, there isn't really a whole lot than can be done, it blooms in the spring, pretty much covers everything, and then dies off in the July/Aug. months, only leaving behind the stalks. I guess dryer springs, which make the water levels lower make the blooms more prevalent.
At any rate, is is something to keep a close eye on. the Delaware's crystal clear water, and polished rocky bottom is what makes that river so attractive. Rock snot is anything but attractive.