The Green River is an anomally in regards to fishing during high water flows. Being a tailwater fishery with approximately 100,000 trout, we do not see many days of bad fishing.
High water flows occur on the Green River when the flows reach 4,600cfs or above. Currently the river is regulated to not go above 9,000cfs as going above this flow requires opening up the spillway. If the spillway is opened it subjects the Green River to many invasive species, so it is only done in emergency situations. In 1998 the flows reached 10,600cfs and fish were still being caught.
The first 3 days of high water churn up all of the previous years accumulated moss, sand and silt, making it almost impossible to catch fish. After the moss, pine needles, and other debris have flushed out the river fishes great again, with each day opening up more and more clear water. Typically, from about 1 mile below Red Creek Rapid (12 miles below the Dam) the water is too murky to have much success. However, in years with prolonged high flows the river fishes decent on the C Section.
Some years it is possible to have incredible dry fly action, even during extreme high water flows. The video on this page was taken during an epic caddis hatch at 8,600 cfs.
Cicadas are also commonly present during high water and prove to be too tempting of morsels for the trout to just sit on the bottom of the river.
If ample dry flies are not present, the trout will be gorging on small scuds and worms. San Juan Worms, Wire Worms and Wiggly Worms in orange, red, brown, pink and purple are great attractors at these flows and will often be taken over the much smaller scuds. The scuds are typically grey in color with, olive and tan varieties also present. When scuds die they change to pink and orange hues. Most scuds in the Green River are about a size #20, but varieties from size #10-28 can be found. During high flows most of the guides have on 1 or 2 worm patterns and/or a small scud pattern at about 10-12 feet deep.