Entomology
Hatch calendar
Every published river laid out by month, so you can see at a glance which months are thick with hatches and which are dead water.
JanFebMarAprMayJunJulAugSepOctNovDec
| Best months | River | Region | Peak hatch | Season |
|---|---|---|---|---|
| Jan · Feb · Mar · Sep · Oct · Nov | Fryingpan River | Basalt, Colorado, United States | Midges (Chironomidae) | Fishable every day of the year thanks to constant 4–6°C releases |
| Jan · Feb · Mar · Apr | Río Grande | Tierra del Fuego, Argentina | Sea-run brown, streamer | Season runs roughly December to mid-April; the sea-run fish enter from January |
| Jan · Feb · Jun · Oct · Nov · Dec | River Wharfe | Yorkshire Dales, England, United Kingdom | Large Dark Olive (Baetis rhodani) | Trout 3 April to 30 September; grayling 16 June to 14 March, which makes winter the local season |
| Jan · Feb · Mar · Oct · Nov · Dec | South Platte — Deckers and Cheesman | Front Range foothills, Colorado, United States | Midges (Chironomidae) | A year-round urban-adjacent fishery; the canyon is best in winter when crowds thin out |
| Mar · Apr · May · Sep · Oct · Nov | San Juan River | Navajo Dam to Farmington, New Mexico, United States | Midges (Chironomidae) | Fishable twelve months; spring and autumn are the busiest and the best |
| Mar · Apr · Sep · Oct · Nov · Dec | Bighorn River | South-central Montana, United States | Blue-Winged Olive (Baetis) | A winter fishery as much as a summer one; the river is at its most consistent from November to March |
| Apr · May · Jun · Sep · Oct · Nov | White River, Arkansas | Ozark foothills below Bull Shoals Dam, Arkansas, United States | Caddis (Hydropsyche) | Year-round, but the fishing depends entirely on whether Bull Shoals is generating |
| Apr · May · Sep · Oct | Davidson River | Pisgah National Forest, North Carolina, United States | Terrestrials — ants and beetles | Fishable all year; the hatchery-supported reach holds fish through winter |
| Apr · May · Jun · Oct | Penns Creek | Centre and Snyder Counties, Pennsylvania, United States | Green Drake (Ephemera guttulata) | Green Drake in the last week of May defines the year; autumn olives run to November |
| Apr · May · Jun · Oct | Letort Spring Run | Cumberland County, Pennsylvania, United States | Scuds and sowbugs | Best from April to June and again in October; midsummer weed growth makes it nearly unfishable |
| Apr · May · Sep · Oct · Nov | Pere Marquette River | West-central Michigan, United States | Sulphur (Ephemerella invaria) | Two seasons in one river: fall steelhead from October, and spring steelhead through April |
| Apr · May · Jun · Sep | River Test | Hampshire, England, United Kingdom | Grannom caddis (Brachycentrus) | Brown trout from 3 April to 30 September; grayling over the winter on some beats |
| Apr · May · Jun · Sep · Oct | Madison River | Southwest Montana, United States | Spotted Sedge (Hydropsyche) | Fishable all twelve months; the season is defined by whether the salmonfly hatch has started and whether Hebgen is spilling |
| May · Jun · Jul · Sep · Oct | Farmington River | Litchfield County, Connecticut, United States | Sulphur (Ephemerella invaria) | Fishable all year; the Trico and sulphur hatches from June to September are the technical part |
| May · Jun · Sep · Oct · Nov | Deschutes River | Central Oregon, United States | Salmonfly (Pteronarcys) | The stonefly hatch runs mid-May to early June; steelhead arrive late August and hold through winter |
| May · Jun · Sep · Oct · Nov | Traun River | Upper Austria / Salzkammergut, Austria | March Brown (Rhithrogena) | Trout 1 April to 30 September, grayling 1 May to 31 December on most beats |
| May · Jun · Sep · Oct | Beaverkill River | Catskill Mountains, New York, United States | Hendrickson (Ephemerella subvaria) | May and June for dry flies; mid-September to November for streamers and olives |
| May · Jun · Jul · Aug · Sep | Green River below Flaming Gorge | Dutch John, Utah, United States | Caddis (Hydropsyche) | Year-round, with the cicada hatch in late summer the local event of the year |
| May · Jun · Jul · Sep · Oct | Henry's Fork of the Snake | Eastern Idaho, United States | Green Drake (Drunella grandis) | A true twelve-month fishery; the famous hatches are mid-June to mid-July and again in September |
| May · Jun · Jul · Sep | Soča River | Julian Alps, Slovenia | March Brown (Rhithrogena) | Marble trout from 1 April; grayling from 16 May; the season closes at the end of September |
| May · Jun · Jul · Sep | Au Sable River | Northern Lower Michigan, United States | Sulphur (Ephemerella invaria) | The Hex hatch in the last week of June is the event; the trout season closes at the end of September |
| Jun · Jul · Aug · Sep · Oct | Tongariro River | Taupō, North Island, New Zealand | Glow bug / egg pattern | Winter run from June to November is the main event; the river fishes all year on some sections |
| Jul · Aug · Sep · Oct | North Umpqua River | Cascade foothills, Oregon, United States | October Caddis (Dicosmoecus) | Summer steelhead from July, with the fly-only water fishable until the end of October |
| Jul · Aug · Sep · Oct | Yellowstone River | Montana and Wyoming, United States | Salmonfly (Pteronarcys californica) | Closed to protect spawning until the third Saturday in July on much of the Montana reach; late July to October is the season |