A stocked stillwater NE of Jaffray, on the east side of the Kootenay River valley. Provincial hatchery records run back to 1920, and today the lake runs on two clean annual programs: Blackwater-strain rainbow trout every fall, kokanee fry every spring.

Rosen Lake sits NE of Jaffray, on the east side of the Kootenay River valley, in the same country as Tie Lake a few kilometres south. The province's 1952 reconnaissance survey put it at about 73 hectares, dropping to a maximum depth of 12.8 m and averaging 4.3 m across the basin, a shallow-to-moderate stillwater with real shoal-and-drop-off structure rather than a deep, sterile hole.

For an angler judging whether the lake is worth a stop, the release record is the fishing report. Provincial hatchery records run from 1920 to 2026 and log 131 releases into Rosen Lake, totalling over a million fish across four species. Rainbow trout carry the volume: about 865,000 fish over 106 releases since 1920, and the program is still very much alive. The last six autumns (2020 through 2025) have each brought 3,000 Blackwater-strain yearlings, sourced from the Dragon and Premier hatcheries, the same broodstock line that seeds Premier Lake itself.

Kokanee are the other active program: 12 releases totalling about 78,000 fry since 2014, and the last five springs have each brought 7,000 fry, alternating Norbury Creek and Lussier River strain, most recently April 2026. Westslope cutthroat were planted three times between 1923 and 2004 (about 37,500 fish) and brook trout ten times between 1986 and 1995 (about 34,900 fish, Aylmer strain), but neither has been restocked since, so any you catch today are legacy or self-sustaining fish, not a fresh plant.

Rosen Lake fishes as a straightforward put-grow stillwater built around two clean annual cohorts. Work the shoal-and-drop-off structure around the edges rather than the deep middle: hang a chironomid or scud pattern under an indicator over the shoals with chironomid under indicator, then follow hot weather stillwater once summer sets up a thermocline, pushing a Woolly Bugger or balanced leech on a sinking line down the drop into the 12.8 m basin. Chironomids, leeches and scuds cover the general stillwater forage base; the kokanee key on zooplankton and are better covered by trolling a small spoon or fly over deeper water than by sight-fishing the shoals.

No confirmed boat launch, parking area or shoreline access point has been found for Rosen Lake. Treat it as an access-check water: confirm a put-in and any private-land or seasonal restrictions locally near Jaffray before committing a day to it.