Upper Priest River has no individual line in the Region 4 synopsis, so regional stream defaults cover the short BC reach: closed Apr 1–Jun 14, trout/char catch-and-release Nov 1–Mar 31, single barbless hook year-round. The river crosses into Idaho within about 9 km of its BC headwaters, where BC regulations no longer apply and Idaho Fish and Game rules take over.

The river's headwaters sit in BC's Selkirk Mountains, part of a range that extends roughly 326 miles from near Coeur d'Alene, Idaho, north into Canada. Only a short stretch, about 9 km (stream order 5, well down the network toward river scale), lies north of the border before Upper Priest River crosses into Idaho. From there it feeds Upper Priest Lake, connected to Priest Lake by a 2.5-mile no-wake channel known as the Thorofare, and Upper Priest Lake itself sits inside a designated Scenic Area reachable only by boat, foot or mountain bike, even from the Idaho side. The Priest River, measured from Upper Priest Lake, runs roughly 109 km (68 miles) before joining the Pend Oreille River near the town of Priest River, Idaho. That confluence is part of the same Pend Oreille system this vault's Pend-d'Oreille River page covers (the BC reach below Waneta and Seven Mile dams), but the two stretches sit hundreds of kilometres apart with Idaho and Washington state between them, so treat them as separate fisheries rather than one contiguous water.

Provincial fish and stream inventory data records a direct catch of westslope cutthroat trout on the BC reach of Upper Priest River. Bull trout and rainbow trout appear in the wider barrier-connectivity model as reachable habitat, but neither has a confirmed record on this stretch.

The BC reach reads as technical, canyon-confined water, not a casual float: median channel width around 6 m (narrow), median gradient around 3.28% (moderate), peak mean-annual discharge around 1.4 m³/s (low flow), with canyon-confined sections showing walls up to roughly 191 m in DEM terrain data. No guide coverage, fishing report or hatch sample exists for the Canadian side of Upper Priest River, so there's no confident fly-box recommendation to give; a general moving-water approach, dry-dropper through the warm months, nymphing the deeper slots as flows drop, is the honest starting point until direct local knowledge says otherwise. If you're after Priest country's real fishing and access, that's almost entirely on the Idaho side, around Upper Priest Lake and Priest Lake.

No road, trail or launch is confirmed on the BC side of Upper Priest River; the terrain is remote Selkirk backcountry hard against the international boundary. The developed access, camping and boat-launch infrastructure for this river system sits well south, around Priest Lake and Upper Priest Lake in Idaho, reached from within the US rather than from BC.