St Marys Lake Depth Map & Fishing Spots (MT)

Hatch outlook

Grasshoppers (east-side summer)Active window

Typical here: Jul 1 – Oct 15 · until the hard frosts of mid-October; on the Missouri, August hoppers fish mid-river, not the banks

adultall day in high summer, best when afternoon wind knocks bugs onto the water

Pulls fish to the windward grassy banks and edges for months — fish the bank the wind blows ONTO.

The friendliest crossover of the summer: on lakes, drift the windward bank with a bubble-and-foam-hopper — the bubble's splash doesn't hurt a hopper presentation. On rivers, the same rig dead-drifted along the undercut grass banks, or small gold spinners under the banks between rises.

The event happens over grassy banks, undercut edges and windward shorelines

Spruce MothActive window

Typical here: Jul 20 – Aug 31 · a conifer-forest event — it needs fir and lodgepole on the banks, so it's a Rock Creek / Blackfoot / upper Bitterroot specialty

adultmorning through midday — moths don't enter the water willingly — landings are sporadic and near the conifer banks; fish the imitation LOW in the film with minimal floatant, even fully drowned, with a little movement

When the moths show, just about every run produces — large trout key on them so hard that one pattern carries the whole box for two weeks.

Honest limit: a small drowned-surface moth has no lure analog. The workable rig is a casting bubble with a drowned moth pattern along the timbered banks in the morning; otherwise fish spinners early and late and leave the moth window to the film.

2–3 weeks at best, and day-to-day — fish key on the moths when they show and vanish with them

The event happens over banks under conifers — the moths rarely reach mid-river

Recommendations come from depth structure and seasonal species behavior. Treat them as a starting point, not a guarantee. Contours here are interpolated from real agency depth surveys (state DNR / USACE). Never use for navigation. Always check local regulations.

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Recent catches at St Marys Lake

Shared by DepthScout anglers. Exact spots stay private, always.

No shared catches here yet — be the first.Log a catch from the map above and share it to put St Marys Lake on the board.

Fishing St Marys Lake: what the data says

244-acre lake in Lake County, Montana. The lake tops out around 240 ft. The depth chart is built from real state fisheries GPS surveys, so the humps, channels and drop-offs you see are measured, not guessed. What the data behind the map says about each species, season by season:

St Marys Lake maps at 244 acres behind 3.1 miles of shoreline. Its 1.4 shoreline index means few bank features; the contours below do the pattern work. 0% of the surface is littoral (under ~15 ft) — cover, weeds and forage water. Figure 1.4 mi of water from one end to the other, 0.4 mi at the beam. Lake County claims this one. Mission Reservoir, In Part sits 6 mi northwest — the closest neighbouring chart.

Brook Trout fishing at St Marys Lake

When the water first warms, brook trout slide up into 2 to 15 ft. Summer is a 10 to 30 ft game here, winter a 3 to 20 ft one. Start at Shallow bay flat. It's a feeding flat holding about 22 ft of water and rates good come winter. The feeding windows run early morning and the evening. Keep a small spoon fished deep or a trolled lake-clear wobbler + worm rigged through the warm months.

Season	Depth	Best window	Start at	Go-to baits
Spring	2 to 15 ft	dawn & dusk	open water	Small inline spinner (gold), Tiny spoon
Summer	10 to 30 ft	dawn & dusk	open water	Small spoon fished deep, Trolled lake-clear wobbler + worm
Fall	2 to 15 ft	midday & dawn	open water	Small spoon (orange), Spinner
Winter	3 to 20 ft	dawn	Shallow bay flat (22 ft)	Small jigging spoon, Tungsten jig + plastic

Cutthroat Trout fishing at St Marys Lake

Start shallow in spring: cutthroat trout sit in 3 to 15 ft that time of year. Summer pushes them deeper, 10 to 35 ft, and winter fish settle into 10 to 40 ft. The spot to know is Main-lake point, a point in about 21 ft of water that rates prime for cutthroat trout in fall. Warm-month bites cluster around early morning and the evening. Throw a trolled spoon (small) or an inline spinner until the fish tell you otherwise.

Season	Depth	Best window	Start at	Go-to baits
Spring	3 to 15 ft	dawn & dusk	open water	Inline spinner (silver/gold), Small spoon
Summer	10 to 35 ft	dawn & dusk	Main-lake point (21 ft)	Trolled spoon (small), Inline spinner
Fall	5 to 25 ft	dawn & dusk	Main-lake point (21 ft)	Casting spoon, Inline spinner
Winter	10 to 40 ft	dawn	Break off the point (40 ft)	Small jigging spoon, Marabou jig

Rainbow Trout fishing at St Marys Lake

Come spring, look for rainbow trout tight to the bank in 5 to 20 ft. They move out to 8 to 30 ft in summer and finish the year down in 8 to 40 ft. If you only fish one area, make it Break off the point: a drop-off around 40 ft that scores prime in winter. Best bite is 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 (21 ft)	Inline spinner (silver), Small spoon
Summer	8 to 30 ft	dawn & dusk	Main-lake point (21 ft)	Dodger + spoon (deep troll), Flutter spoon
Fall	10 to 35 ft	dawn & dusk	Main-lake point (21 ft)	Casting spoon, Jerkbait over shoals
Winter	8 to 40 ft	dawn	Break off the point (40 ft)	Jigging spoon, Tube jig (white)

Notable structure

Structure-wise the chart holds 7 features, led in depth by Deep basin at roughly 240 ft.

Deep basin: deep basin, around 240 ft
Shallow feeding flat: feeding flat, around 61 ft
Secondary point: point, around 44 ft
Break off the point: drop-off, around 40 ft
Back-bay flat: feeding flat, around 30 ft
Shallow bay flat: feeding flat, around 22 ft
Main-lake point: point, around 21 ft

St Marys Lake fishing regulations

Season dates, license requirements, and size and bag limits for Montana waters are set by the Montana Fish, Wildlife & Parks — and special regulations can apply to St Marys Lake specifically, so confirm the current rules before you fish.

Check the official Montana fishing regulations →

Common questions

How deep is St Marys Lake?

St Marys Lake is about 240 ft (73 m) deep at its deepest point. The depth chart here comes from real state fisheries GPS surveys, so the contours reflect measured depths.

What fish are in St Marys Lake?

Anglers target brook trout, cutthroat trout, rainbow trout on St Marys Lake.

Where is the best fishing spot on St Marys Lake?

Main-lake point is the top-rated area: a point in about 21 ft of water that rates prime for cutthroat trout in fall. Every other rated spot, per species and season, is on the map above.

When is the best time to fish St Marys Lake?

For brook 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.

What are the fishing regulations for St Marys Lake?

Fishing on St Marys Lake is regulated by the Montana Fish, Wildlife & Parks. Check the official Montana regulations for current license requirements, season dates, and size and bag limits — special regulations can apply to this specific water.

Nearby waters

Mission Reservoir, In Part 6 mi · South Meadow Lake 10 mi · Lake Elsina 10 mi · Mcdonald Lake 11 mi · Rattlesnake Lake #22 11 mi · Lindbergh Lake 12 mi · Fly Lake (Missoula) 13 mi · Lake Marshall 13 mi · Boulder Lake 14 mi · Sanders Lake 14 mi · Colt Lake 14 mi · Little Lake 15 mi

See how St Marys Lake stacks up: best rainbow trout lakes in Montana · best brook trout lakes in Montana · best cutthroat trout lakes in Montana

More water nearby: Lake County fishing maps (12 charts). Browse all Montana fishing maps or see every water on DepthScout. Bathymetry credit: state fisheries survey programs. 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.