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415-acre reservoir near Boulder County. The lake tops out around 299 ft. These contours are modeled — built from the real shoreline and the water's maximum depth — so read them as a guide, never as navigation. What the data behind the map says about each species, season by season:
On the chart, Gross Reservoir draws 415 acres inside 10.6 miles of shoreline. An index of 3.7 puts the bank firmly in maze territory: point after pocket after cove, every one a casting target. About 25% of the surface sits shallower than 15 ft on the modeled chart — that's the weed-and-bait zone. The basin spans about 2 mi end to end and 1.4 mi across at its widest. The water lies in Boulder County. The nearest mapped water is Barker Reservoir, 7 mi to the west.
In spring, muskellunge run shallow here, mostly 3 to 12 ft. Summer pushes them deeper, 8 to 25 ft, and winter fish settle into 15 to 35 ft. Shallow bay flat is the standout, a weed flat at roughly 6 ft, rated prime for spring muskellunge. Time it for the evening and early morning. You won't need more than a double-10 bucktail or a topwater (walk-the-dog / creeper) most summer days.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 3 to 12 ft | dusk | Shallow bay flat (6 ft) | Smaller bucktail (#8 blades), 6" glide bait |
| Summer | 8 to 25 ft | dusk & dawn | Shallow bay flat (6 ft) | Double-10 bucktail, Topwater (walk-the-dog / creeper) |
| Fall | 8 to 30 ft | midday & dusk | Shallow bay flat (6 ft) | Big rubber (Bull Dawg style), 10"+ glide bait |
| Winter | 15 to 35 ft | midday | Deep basin (254 ft) | Large rubber, crawled slow |
In spring, kokanee run shallow here, mostly 10 to 30 ft. Midsummer fish sit out in 30 to 70 ft before dropping to 20 to 80 ft for winter. Spring kokanee concentrate at Deep basin, a good-rated deep basin around 254 ft. Fish it in early morning and you'll meet the bite. You won't need more than a dodger + pink/orange squid on downrigger or a kokanee bug + corn most summer days.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 10 to 30 ft | dawn | Deep basin (254 ft) | Small dodger + squid (pink), Wedding-ring spinner + corn |
| Summer | 30 to 70 ft | dawn | Deep basin (254 ft) | Dodger + pink/orange squid on downrigger, Kokanee bug + corn |
| Fall | 5 to 40 ft | dawn | open water | Dodger + squid (deeper red/purple), Small spoon |
| Winter | 20 to 80 ft | dawn | Deep basin (254 ft) | Small glow jig + corn or maggot, Tiny spoon |
In spring, brook trout run shallow here, mostly 2 to 15 ft. Midsummer fish sit out in 10 to 30 ft before dropping to 3 to 20 ft for winter. Spring brook trout concentrate at Shallow bay flat, a good-rated weed flat around 6 ft. Fish it in early morning and the evening and you'll meet the bite. You won't need more than a small spoon fished deep or a trolled lake-clear wobbler + worm most summer days.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 2 to 15 ft | dawn & dusk | Shallow bay flat (6 ft) | 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 (6 ft) | Small jigging spoon, Tungsten jig + plastic |
Come spring, look for brown trout tight to the bank in 3 to 25 ft. They move out to 25 to 60 ft in summer and finish the year down in 5 to 35 ft. If you only fish one area, make it Break off the point: a drop-off around 135 ft that scores good in summer. Best bite is after dark and early morning. A spoon at the thermocline or a deep stickbait (night) is the honest summer answer here.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 3 to 25 ft | dawn & dusk | open water | Stickbait off planer boards (shallow), Small spoon along mud lines |
| Summer | 25 to 60 ft | night & dawn | Break off the point (135 ft) | Spoon at the thermocline, Deep stickbait (night) |
| Fall | 5 to 30 ft | dusk & dawn | open water | Jerkbait over gravel, Casting spoon |
| Winter | 5 to 35 ft | dawn | Break off the point (135 ft) | Jigging spoon, Small stickbait (slow) |
Spring puts lake trout in skinny water — 10 to 40 ft is the zone. As the season builds they drop to 50 to 120 ft, wintering in 20 to 80 ft. Summer lake trout concentrate at Break off the point, a good-rated drop-off around 135 ft. Warm-month bites cluster around early morning. A white tube jig (deep) or a magnum spoon on downrigger covers the summer program.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 10 to 40 ft | dawn & dusk | Main-lake point (75 ft) | Casting spoon over shoals, Jerkbait (shallow) |
| Summer | 50 to 120 ft | dawn | Break off the point (135 ft) | White tube jig (deep), Magnum spoon on downrigger |
| Fall | 10 to 50 ft | dusk & dawn | open water | Heavy casting spoon, Jigging rap over reefs |
| Winter | 20 to 80 ft | dawn | Deep basin (254 ft) | White tube jig, Airplane jig |
Spring puts rainbow trout in skinny water — 5 to 20 ft is the zone. Warm water sends them out to 8 to 30 ft; cold water stacks them in 8 to 40 ft. Shallow bay flat is the standout, a weed flat at roughly 6 ft, rated good for spring rainbow trout. Plan around early morning and the evening in the warm months. A dodger + spoon (deep troll) or a flutter spoon covers the summer program.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 5 to 20 ft | dawn & dusk | Shallow bay flat (6 ft) | Inline spinner (silver), Small spoon |
| Summer | 8 to 30 ft | dawn & dusk | Shallow bay flat (6 ft) | Dodger + spoon (deep troll), Flutter spoon |
| Fall | 10 to 35 ft | dawn & dusk | open water | Casting spoon, Jerkbait over shoals |
| Winter | 8 to 40 ft | dawn | Break off the point (135 ft) | Jigging spoon, Tube jig (white) |
Gross Reservoir also holds cutthroat trout (10 to 35 ft in summer), splake (25 to 60 ft in summer). Pick any of them on the map above for rated spots and bait picks.
The chart marks 6 structure features on Gross Reservoir; the deepest is Deep basin at about 254 ft.
Access data: OpenStreetMap contributors (ODbL) — community-mapped launches. Confirm conditions and fees locally before you launch.
Season dates, license requirements, and size and bag limits for Colorado waters are set by the Colorado Parks & Wildlife — and special regulations can apply to Gross Reservoir specifically, so confirm the current rules before you fish.
Check the official Colorado fishing regulations →
Gross Reservoir is about 299 ft (91 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 muskellunge, kokanee, brook trout, brown trout, lake trout, rainbow trout, cutthroat trout, splake on Gross Reservoir.
Shallow bay flat is the top-rated area: a weed flat in about 6 ft of water that rates prime for muskellunge in spring. Every other rated spot, per species and season, is on the map above.
For muskellunge, the summer bite is best in the evening and early morning. Each species page section below lists the seasonal windows, and the map shows a live NOW badge when you're inside one.
Fishing on Gross Reservoir is regulated by the Colorado Parks & Wildlife. Check the official Colorado regulations for current license requirements, season dates, and size and bag limits — special regulations can apply to this specific water.
Barker Reservoir 7 mi · Arvada Reservoir 12 mi · Boulder City Reservoir 12 mi · Waneka Lake 14 mi · Standley Lake 14 mi · Woodland Lake 15 mi · Diamond Lake Upper 16 mi · Bob Lake 17 mi · Crater Lake #1, Upper 17 mi · Button Rock Res 19 mi · Jim Baker Reservoir 20 mi · Berkeley Lake 21 mi
See how Gross Reservoir stacks up: best rainbow trout lakes in Colorado · best lake trout lakes in Colorado · best brown trout lakes in Colorado · best brook trout lakes in Colorado
More water nearby: Boulder County fishing maps (8 charts). Browse all Colorado 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.