The Trout Hatch Calendar: What Hatches When, Month by Month
Ask a guide what month it is and they won't say May — they'll say "caddis, maybe the start of stones." Trout live on a calendar written in insects, and once you can read it, you stop guessing and start predicting. This is that calendar: the nine hatches that matter, when each one starts, when it peaks, and the patterns that match it.
Full bar = active months · Bright core = peak weeks
Timing shifts 2–4 weeks earlier on Pacific & southern streams, later in the Rockies & northern Canada
March & April: the little stuff first
Cold water, small bugs, slow drifts. Midges are the only game most mornings — a Zebra Midge under an indicator, or a Griffith's Gnat when you spot clusters dimpling the surface. On gray, drizzly afternoons the first Blue-Winged Olives show and trout slide onto the soft edges to sip them. Keep it small (#18–#24), keep it light (6X–7X), and fish the warmest two hours of the day.
May & June: the big-bug window
This is the best dry-fly fishing of the year, full stop. Caddis explode over riffly water in the late afternoon — skate an Elk Hair Caddis and hang on. March Browns and PMDs fill the midday hours, and on western freestones — BC's Thompson, Montana's Madison, Alberta's Crowsnest — the giant salmonflies crawl out, when a #4 Stimulator is the closest thing to cheating this sport allows. If you only get one month on the water, make it this one.
July & August: dawn patrol and land-born protein
Hatches thin out in the heat, so change clocks. Tricos at first light — a spinner fall over glassy water, #22s on 6X, the most technical fishing of the year. Then the sun climbs and terrestrials take over: ants, beetles, and hoppers plopped tight to undercut banks and overhanging grass. Wind is your friend now — it blows lunch into the river.
September to November: the second act
Cooler nights wake the Blue-Winged Olives back up, and fall hatches happen in miserable, perfect weather — drizzle, fog, no crowds. Tailwaters like the Bow below Calgary or southern Ontario's Grand River shine now, midges return to the menu, and pre-spawn brown trout turn aggressive and territorial — your cue to strip streamers through the pools you walked past all summer.
A calendar tells you what's hatching; our match-the-hatch cheat sheet tells you what size and tippet to match it with. Read the season, tie on the right bug, and go get your month back.
Keep the momentum going:
Pack for the season's checklist