The Portal, and why the creek runs brown
Just downstream of the Shandaken Town Hall a concrete outlet dumps Schoharie Reservoir water into the Esopus. That is the Shandaken Tunnel Portal, opened on February 9, 1924, and it can deliver up to 600 million gallons a day of mostly cold water from one valley north. When the Portal is running it governs flow, temperature and clarity from Allaben all the way to the Ashokan Reservoir, and the problem, as Tony Bonavist put it in the River Reporter, is that the Schoharie turns brown after heavy rain because of the clay along its tributaries, and the tunnel carries that color straight into the creek. Off-color water is why the Esopus draws fewer anglers than the Beaverkill and why, by most accounts, its hatches are thinner.
The upside is cold water in August when the freestones around it are too warm, plus wild fish. DEC manages the whole upper creek on natural reproduction with no stocking, and the rainbows below Lost Clove Road, mostly 8 to 12 inches by DEC's survey description, are the descendants of fish that have held in this creek since they were brought from California in the late 1800s. There is a decent population of browns too, and brook trout in the headwaters and tributaries.
Isonychia, twice a year
This is the one hatch the Esopus does better than any other Catskill river, by Bonavist's account and DEC's. There are two emergences: one toward the end of June that starts around 6 p.m., and a fall hatch that begins in September, runs into October and comes off around 2 p.m. The June flies are bigger, about a size 12. Isonychia nymphs crawl to the bank and hatch on the stones rather than in the film, so unless a breeze blows the duns back onto the water there is little surface feeding; on a windy October afternoon above the Five Arches Bridge Bonavist and two friends fished Art Flick's size 12 Dun Variant to rising fish and did well. A swung Isonychia nymph or a Leadwing Coachman covers the other days.
Before the Isos the creek follows the standard Catskill order. The Big Y chart for the Esopus has Quill Gordons and Red Quills from April 1, Hendricksons and Blue Quills from mid-April to mid-May, March Browns, Gray Fox, Light Cahills and Sulphurs from May 10 into June and July, a green caddis in May and June, and brown caddis in August. DEC names the Isonychia, olive and Sulphur mayflies and the late-season stoneflies as the hatches that matter most here.
Route 28 from Big Indian to Boiceville
Route 28 follows the creek the length of the upper Esopus, and the towns are your mile markers. Above the Lost Clove Road bridge in Big Indian the water is pocket water with smaller fish and access limited to a half mile of Forest Preserve along Oliverea Road above Giant Ledge Stream. Below Lost Clove the creek widens as Birch Creek, Bushnellsville Creek, Fox Hollow and Peck Hollow come in, and access opens up through Forest Preserve, New York City DEP land, county parcels and public fishing rights easements. Creek Side Road in Shandaken gets you on the water above the Portal. In Phoenicia the mouth of Woodland Valley Creek is a well-known spot where rainbows stack below the confluence, and Esopus Creel, the fly shop at 5579 Route 28, is the place for a current read on the Portal. From Mount Tremper to Boiceville the creek runs bigger, with the largest pools and the largest fish, and the Coldbrook gauge sits at the bottom of it.
Two access notes. NYC DEP land needs a DEP access permit, and the creek from Phoenicia down is tube and raft water on summer days, so fish early or fish above town.
Coldbrook at 200 to 400 cfs
Guide Recommended's write-up gives 200 to 400 cfs as the flow to look for, and DEC lists the Coldbrook Road gauge in Boiceville as the downstream reference alongside Allaben and Lost Clove. Above 400 the casting lanes shrink and the wading gets harder in a creek that is mostly cobble and fast water. The long-term record at Coldbrook has monthly medians near 1,150 cfs in April, 790 in May, 550 in June and 340 to 440 from July through October, so the window opens in late June and stays open most of the summer and fall unless the Portal is wide open or a storm hits. Check the Portal gauge, USGS 01362230, next to Coldbrook; if the tunnel is releasing hard after rain the creek below Allaben will be high and brown regardless of what fell on the Catskills. In summer, scan the previous day's hourly temperatures at Coldbrook and skip the lower creek above 70 degrees.
Wild Quality rules below Lost Clove Road
From the Ashokan Reservoir upstream to the confluence with Lost Clove Creek at Big Indian the Esopus is a Wild Quality reach under the NYSDEC inland trout regulations: April 1 through October 15, three trout a day with no more than one longer than 12 inches, then October 16 through March 31 catch and release only with artificial lures. Bait is legal during the harvest season. Upstream of Lost Clove Road the creek and all of its tributaries, Birch Creek, Stony Clove, Woodland Valley Creek and the rest, are under the statewide Wild rule, five fish with no more than two over 12 inches in the same open season and the same winter catch-and-release. The old November 30 closing date still quoted in some guides is gone. The lower Esopus below the Ashokan dam is managed as warmwater and is a different fishery altogether.