Umpqua National Forest, Oregon: a rebuilt rainbow fishery below Mount Thielsen
Overview
Diamond Lake sits at about 5,180 feet in the Umpqua National Forest of southern Oregon, just north of Crater Lake, a 3,000-acre natural lake no more than 52 feet deep, with Mount Thielsen's spire on the east side and Mount Bailey on the west. Its story is a cautionary one. Illegally introduced tui chub took over the lake, wrecked water quality and collapsed the trout fishery; in September 2006 ODFW treated the entire lake with rotenone, killing an estimated 90 million chub, then restocked rainbows. The comeback was fast, and within a few years Diamond was again one of Oregon's most productive trout lakes. Then in October 2015 a single tui chub turned up in a survey net. ODFW's answer was sterile tiger trout, first stocked in June 2016 to eat chub and any other illegal minnows, alongside brown trout; both are now catch-and-release, and the reminder that live bait is how the chub arrived is posted everywhere. For anglers, the shallow, weedy bottom grows chironomids, Callibaetis and leeches in quantity. The best fishing is April, May and early June after ice-off, when chironomid hatches can be enormous and Callibaetis begin to show, and again in fall when the campgrounds empty. Summer mornings still fish, mostly deeper. The lake is open all year under the general Southwest Zone rules, the resort rents boats, and the North Umpqua's fly-only water is under an hour west.
Hatching now · October
Chironomid/Midge
PEAKCallibaetis
ACTIVELeech
PEAKAngler reports
Hatch chart
| Insect | J | F | M | A | M | J | J | A | S | O | N | D |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chironomid/Midge | January: absent | February: absent | March: active | April: peak | May: peak | June: peak | July: active | August: active | September: peak | October: peak | November: active | December: absent |
| Callibaetis | January: absent | February: absent | March: absent | April: absent | May: active | June: peak | July: peak | August: peak | September: peak | October: active | November: absent | December: absent |
| Damselfly | January: absent | February: absent | March: absent | April: absent | May: absent | June: active | July: peak | August: peak | September: active | October: absent | November: absent | December: absent |
| Leech | January: absent | February: absent | March: active | April: peak | May: peak | June: peak | July: active | August: active | September: peak | October: peak | November: active | December: absent |
Timing checked against
Chironomid confirmed: Fly & Field lists chironomids, callibaetis and leeches as the food sources and says the best fishing is April, May and early June after ice-out plus fall; Caddis Fly Shop reports 'epic chironomid hatches' in mid-May 2013 and a strong hatch in late May 2024. Leech (balanced leeches, buggers) confirmed by both. Damselfly is mentioned only in passing (a commenter fishes damsel nymphs 'if there are damsels going'), so that row was left unchanged.
How to fish it
Diamond Lake is open all year. The ODFW Southwest Zone rules for lakes apply: 5 trout per day, 8-inch minimum, only one over 20 inches, with three daily limits in possession. Tiger trout and brown trout are catch-and-release only. Live bait fish are illegal statewide in Oregon, and this lake is the reason that rule matters.
An Oregon angling license is required at 12 and older. Check the current Oregon Sport Fishing Regulations for the Southwest Zone before you go.
Facts checked against
Added the part of the story the copy left out: tui chub were found again in 2015 and ODFW has stocked sterile tiger trout since 2016, with tiger and brown trout now catch-and-release. Removed the unsourced 2-4 pound and 8-pound figures and the claim of special size limits and gear sections. Fixed the viewpoint (Thielsen is east of the lake, so the view is from the west shore). Confirmed the 2006 rotenone treatment, roughly 3,000 acres, 52-foot depth and the spring chironomid fishing.