No Castor Creek-specific exception appears in the Region 4 synopsis, so regional defaults apply: closed to fishing Apr 1 to Jun 14, trout and char catch-and-release from Nov 1 to Mar 31, and a single barbless hook required all year. Confirm the current synopsis and any in-season notices before fishing.

The Forster-Frances drainage is glacier- and alpine-lake fed, steep near its headwaters, and many of its smaller tributaries run low or seasonally dry by late summer. Castor fits that pattern: a minor tributary with a single recorded cutthroat rather than a mapped, continuously fish-bearing stream. An unnamed side tributary to Castor Creek was flagged for follow-up sampling because low-flow conditions at the time of survey left its fish-bearing status uncertain, a caution worth carrying onto Castor's own smaller water too.

With one fish record and no dedicated guide coverage, Castor Creek is a water to scout rather than plan a trip around. If you find fishable water, treat it as classic small mountain-creek fishing: short drifts through plunge pools and pocket water behind boulders and logjams, working upstream on foot. Kootenay Troutfitters is the nearest established guide presence in the Columbia Valley, though no source ties them specifically to Castor Creek.

Fish it with the same cold mountain-creek box that covers the wider Forster-Frances system: a Royal Wulff or Adams on top, an Elk Hair Caddis through summer hatches, and a Hare's Ear or Prince Nymph with a small Woolly Bugger for the deeper pockets. Caddisflies, mayflies, small stoneflies and summer terrestrials make up the food base across the Frances and Forster drainages, though no Castor-specific hatch timing has been recorded.

There is no named trailhead or put-in confirmed for Castor Creek itself. The wider Forster-Frances system is reached from the Radium Hot Springs or Brisco crossings on Highway 95, via Forster Main, Westside Main and Redrock Road, with the Frances Creek Forest Service Road running toward Hurst Creek. The secondary logging roads through this country are complex and in variable condition, so a current map or GPS track is worth carrying before heading in, and confirm any crossing sits on public rather than private or active industrial ground.