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Rating depth structure for rainbow trout.
Recent public catches load as you reach this section.
149-acre lake in Cariboo Regional District, British Columbia. The lake tops out around 36 ft. Depth here is modeled from the true shoreline and max depth rather than surveyed; use it to plan, not to navigate. Every species below gets its seasonal read from the same numbers driving the chart.
Big Onion Lake maps at 149 acres behind 5.4 miles of shoreline, broken up by an island. With a shoreline index of 3.2, this water is all arms and coves — edge habitat well beyond its acreage. The shallow band under 15 ft claims about 76% of the surface on the model — that's where the groceries are. Figure 1.7 mi of water from one end to the other, 0.4 mi at the beam. It sits in Cariboo Regional District. Its nearest charted neighbour, Fish Lake, is 3 mi to the north.
Come spring, look for rainbow trout tight to the bank in 5 to 20 ft. Expect a summer slide to 8 to 30 ft, then a winter hold in 7 to 36 ft. Start at Main-lake point. It's a point holding about 9 ft of water and rates prime come spring. Prime time lands in early morning and the evening. A dodger + spoon (deep troll) or a flutter spoon is the honest summer answer here.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 5 to 20 ft | dawn & dusk | Main-lake point (9 ft) | Inline spinner (silver), Small spoon |
| Summer | 8 to 30 ft | dawn & dusk | Main-lake point (9 ft) | Dodger + spoon (deep troll), Flutter spoon |
| Fall | 10 to 35 ft | dawn & dusk | Main-lake point (9 ft) | Casting spoon, Jerkbait over shoals |
| Winter | 7 to 36 ft | dawn | Deep basin (31 ft) | Jigging spoon, Tube jig (white) |
Structure-wise the chart holds 5 features, led in depth by Deep basin at roughly 31 ft.
Season dates, license requirements, and size and bag limits for British Columbia waters are set by the BC freshwater fishing synopsis — and special regulations can apply to Big Onion Lake specifically, so confirm the current rules before you fish.
Check the official British Columbia fishing regulations →
Big Onion Lake is about 36 ft (11 m) deep at its deepest point. The contours here are modeled from the water's real shape and maximum depth, so treat them as a rough guide.
Anglers target rainbow trout on Big Onion Lake.
Main-lake point is the top-rated area: a point in about 9 ft of water that rates prime for rainbow trout in spring. Open the map above to see every rated spot for each species and season.
For rainbow trout, the summer bite is best in early morning and the evening. Each species page section below lists the seasonal windows, and the map shows a live NOW badge when you're inside one.
Fishing on Big Onion Lake is regulated by the BC freshwater fishing synopsis. Check the official British Columbia regulations for current license requirements, season dates, and size and bag limits — special regulations can apply to this specific water.
Fish Lake 3 mi · Wasp Lake 4 mi · Lastman Lake 6 mi · Big Lake 9 mi · Vick Lake 12 mi · Fishem Lake 12 mi · Konni Lake 12 mi · Vedan Lake 12 mi · Elkin Lake 15 mi · Chaunigan Lake 16 mi · Kloakut Lake 17 mi · Chilko Lake 21 mi
See how Big Onion Lake stacks up: best rainbow trout lakes in British Columbia
More water nearby: Cariboo Regional District fishing maps (445 charts). Browse all British Columbia fishing maps or see every water on DepthScout. How we build these maps. Fish here with a sonar unit that logs? Send us your depth data and we'll improve this chart, credited to you. For fishing guidance only, never navigation.