Ramblings of a Catskill Fly Fisher

Isonychia mayfly hatches on the Esopus Creek

Posted 9/20/23

The Esopus Creek begins its journey from its source at Winnisook Lake on Slide Mountain in the Catskill Mountains, before joining the Hudson Estuary near Saugerties some 65 miles away.

The …

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Ramblings of a Catskill Fly Fisher

Isonychia mayfly hatches on the Esopus Creek


The Esopus Creek begins its journey from its source at Winnisook Lake on Slide Mountain in the Catskill Mountains, before joining the Hudson Estuary near Saugerties some 65 miles away.

The headwaters and several tributaries support wild  populations of Eastern brook trout. Those tributaries were subject to overfishing and logging for hemlock bark during the 1800s.

Both overfishing and logging had devastating impacts on those wild brook trout populations.

The Esopus proper supports both wild rainbow and brown trout fisheries. Since the implementation of the new trout stream fishing regulations in 2021, the Esopus is no longer stocked.

Before the construction of Ashokan and Schoharie reservoirs, the Esopus was a typical freestone Catskill River, subject to the vagaries of the weather. That meant it flooded in spring, and saw low flows with high water temperatures during the summer. The Esopus was not a trout fishery below Shandaken.

Then in 1907, New York City, in its quest for a new water supply to quench the thirst of a growing population, began construction of the Ashokan Reservoir in the towns of Hurley and Olive. Construction was completed in 1915.

But that was not the end of the Catskill water supply story. In 1926, New York City brought Schoharie (Gilboa) Reservoir online, because Ashokan and its watershed were not adequate to meet the city’s future water needs.

Schoharie Reservoir is linked to the Esopus Creek and Ashokan Reservoir via the Shandaken Tunnel, which is 18 miles long. Up until 1977, New York City opened and closed the tunnel, so it was either on or off. That caused the stranding of a lot of brown and rainbow trout. With the passage of the water release legislation in 1976, the city was mandated to open the tunnel in 40 cubic feet per second (cfs) increments and close it in 20 cfs increments.

The 1976 legislation also caused the city to maintain a combined minimum flow of 248 cfs,  measured at the Shandaken gage.

Once the Schoharie system was put into operation, the Esopus ecosystem below the tunnel entrance was changed dramatically and forever. Cold water from the Schoharie Reservoir made the Esopus Creek a trout fishery all the way to the Ashokan Reservoir, 11 miles distant.

That being said, the discharge of cool water from the Schoharie into the Esopus came with a price. The upper Schoharie watershed is inundated with red clay deposits all along its tributaries. So during heavy rain, that clay is transported into the Schoharie Reservoir and ultimately the Esopus Creek via the Shandaken tunnel.

So while the addition of cool bottom water from Schoharie is a positive, the turbidity created from red clay is a negative. During rainy conditions, the Esopus Creek runs reddish-brown.

As a result, the Esopus is not aesthetically pleasing as a fishery, but more importantly, the turbid water has a significant impact on the aquatic ecosystem of the river.

Following is a quote from the New York State Conservation Department's 26th annual report, in 1936, “A Biological Survey Of The Lower Hudson Watershed, “The Stream [Esopus] between Ashokan Reservoir and tunnel entrance is profoundly affected by the addition of water supplied by Gilboa [Schoharie Reservoir].”

As a result of the discharge of turbid water, the Esopus does not have the most prolific fly hatches when compared with other Catskill Rivers. That is with the exception of the mayfly, Isonychia bicolor, commonly known as lead wing coachman or whirling dun. For whatever reason—turbidity included—in the Esopus Creek, Isonychia hatches are the best in the Catskills, and that includes those in the Beaver Kill, Willowemoc and the Delaware.

And Isonychia has two emergences: one in late June and the other in September. The September hatch can run into October. The June hatch begins around 6 p.m., while the fall hatch starts about 2 p.m. The June flies are larger, about a size 12; the fall flies are a bit smaller.

Both hatches are prolific, with the nymphs—being rapid swimmers—climbing onto shoreline stones, where the final emergence to the dun stage takes place. Anglers fortunate enough to be on the river during either of these hatches will observe hundreds of nymphal cases shed on streamside rocks.

Since the flies hatch out of the water, there’s not as much surface feeding when compared with other mayfly hatches. In addition, the trout chase the nymphs as they migrate toward shore. Spinner falls might provide the best dry fly fishing.

Our famous Catskill fly tier, Art Flick, created the dry fly pattern used to imitate the Isonychia duns. He named that fly the Whirling Dun.

Historically, anglers did well fishing this hatch, with lead wing coachman wet flies. They would cast their flies across and downstream, allowing them to “swing” with the current. Strikes would occur at the end of the swing.

My friend Bert fished the dry fly in this manner too, letting it float before the current pulled it under. That’s when strikes would occur and they could be vicious.

Two friends, Ed and Jack, joined me one early October day on the Esopus, during the afternoon Isonychia hatch. We had good sport with medium-sized rainbows that came readily to our flies on that fine day.

Anglers who fish the Esopus should set some time aside and be on the river during this fall’s hatch. The Esopus Isonychia hatch provides the best fly fishing opportunity of the year on that river.


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