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749-acre reservoir near Weld County. The lake tops out around 28 ft. Depth here is modeled from the true shoreline and max depth rather than surveyed; use it to plan, not to navigate. Here is how the season plays out for each species, straight from the data behind the map.
Union Reservoir maps at 688 acres behind 4.5 miles of shoreline. Nearly circular (index 1.2), so the story is the bottom, not the bank. Roughly 67% of the water is 15 ft or less as modeled, the band where the food chain lives. End to end it runs roughly 1.5 mi, about 1.2 mi across. Weld County claims this one. If the bite dies, Milavec Reservoir is 6 mi to the southeast.
Spring largemouth bass on Union Reservoir hold shallow, usually 2 to 10 ft. By summer they slide out to 8 to 20 ft, and by winter most fish are in 8 to 28 ft. The chart's best answer is Shallow bay flat — weed flat, 3 ft, prime for spring. Prime time lands in early morning and the evening. The summer box starts with a texas-rigged 10" worm or a deep-diving crankbait.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 2 to 10 ft | dawn & dusk | Shallow bay flat (3 ft) | Spinnerbait, Chatterbait |
| Summer | 8 to 20 ft | dawn & dusk | Break off the point (13 ft) | Texas-rigged 10" worm, Deep-diving crankbait |
| Fall | 4 to 15 ft | midday & dawn | Main-lake point (8 ft) | Squarebill crankbait (shad), Spinnerbait |
| Winter | 8 to 28 ft | midday | Break off the point (13 ft) | Blade bait, Jigging spoon |
Early season smallmouth bass use the shallows, holding in 3 to 12 ft. Expect a summer slide to 8 to 28 ft, then a winter hold in 8 to 28 ft. Put Main-lake point first on the milk run — a point near 8 ft that grades prime for fall. In summer the feeding windows fall in early morning and the evening. Tie on a drop shot (goby/minnow) or a ned rig and you're in the game.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 3 to 12 ft | dawn & dusk | Main-lake point (8 ft) | Ned rig, Tube jig |
| Summer | 8 to 28 ft | dawn & dusk | Break off the point (13 ft) | Drop shot (goby/minnow), Ned rig |
| Fall | 8 to 25 ft | midday & dawn | Main-lake point (8 ft) | Jerkbait, Blade bait |
| Winter | 8 to 28 ft | midday | Break off the point (13 ft) | Blade bait, Hair jig |
Early season white bass & hybrids use the shallows, holding in 3 to 15 ft. Expect a summer slide to 8 to 28 ft, then a winter hold in 8 to 28 ft. Put Main-lake point first on the milk run — a point near 8 ft that grades prime for fall. In summer the feeding windows fall in early morning and the evening. Tie on a jigging spoon or a topwater (when schooling) and you're in the game.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 3 to 15 ft | midday & dawn | Main-lake point (8 ft) | Rooster tail / inline spinner, Curly-tail jig (white/chartreuse) |
| Summer | 8 to 28 ft | dawn & dusk | Main-lake point (8 ft) | Jigging spoon, Topwater (when schooling) |
| Fall | 8 to 25 ft | midday & dawn | Main-lake point (8 ft) | Small blade bait, Jigging spoon |
| Winter | 8 to 28 ft | midday | Deep basin (24 ft) | Jigging spoon, Blade bait (vertical) |
When the water first warms, common carp slide up into 2 to 10 ft. Summer is a 3 to 15 ft game here, winter an 8 to 28 ft one. Start at Shallow bay flat. It's a weed flat holding about 3 ft of water and rates prime come spring. The feeding windows run early morning and the evening.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 2 to 10 ft | midday & dawn | Shallow bay flat (3 ft) | |
| Summer | 3 to 15 ft | dawn & dusk | Shallow bay flat (3 ft) | |
| Fall | 5 to 18 ft | midday | Shallow bay flat (3 ft) | |
| Winter | 8 to 28 ft | midday | Deep basin (24 ft) |
Spring channel catfish on Union Reservoir hold shallow, usually 3 to 12 ft. By summer they slide out to 8 to 25 ft, and by winter most fish are in 8 to 28 ft. The chart's best answer is Deep basin — deep basin, 24 ft, prime for winter. Prime time lands in after dark and the evening.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 3 to 12 ft | dusk | Shallow bay flat (3 ft) | |
| Summer | 8 to 25 ft | night & dusk | Deep basin (24 ft) | |
| Fall | 8 to 28 ft | dusk | Deep basin (24 ft) | |
| Winter | 8 to 28 ft | midday | Deep basin (24 ft) |
Early season crappie use the shallows, holding in 2 to 8 ft. Expect a summer slide to 10 to 25 ft, then a winter hold in 8 to 28 ft. Put Deep basin first on the milk run — a deep basin near 24 ft that grades prime for winter. In summer the feeding windows fall in early morning and the evening. Tie on a jig trolled/spider-rigged or a small crankbait (trolled) and you're in the game.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 2 to 8 ft | midday & dawn | Shallow bay flat (3 ft) | 1/16 oz jig + tube, Curly-tail grub |
| Summer | 10 to 25 ft | dawn & dusk | Break off the point (13 ft) | Jig trolled/spider-rigged, Small crankbait (trolled) |
| Fall | 8 to 20 ft | dawn | Break off the point (13 ft) | Jig + minnow combo, Small swimbait (1.5-2") |
| Winter | 8 to 28 ft | midday | Deep basin (24 ft) | Tungsten jig + soft plastic, Tiny jigging spoon |
Union Reservoir also holds walleye (8 to 28 ft in summer), yellow perch (8 to 28 ft in summer), bluegill (4 to 15 ft in summer), rainbow trout (7 to 28 ft in summer). Pick any of them on the map above for rated spots and bait picks.
The chart marks 8 structure features on Union Reservoir; the deepest is Deep basin at about 24 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 Union Reservoir specifically, so confirm the current rules before you fish.
Check the official Colorado fishing regulations →
Union Reservoir is about 28 ft (9 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 largemouth bass, smallmouth bass, white bass & hybrids, common carp, channel catfish, crappie, walleye, yellow perch, bluegill, rainbow trout on Union Reservoir.
Shallow bay flat is the top-rated area: a weed flat in about 3 ft of water that rates prime for largemouth bass in spring. Scroll up to the map for the complete spot list by species and season.
For largemouth bass, 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 Union 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.
Milavec Reservoir 6 mi · Boulder City Reservoir 12 mi · Waneka Lake 13 mi · Lon Hagler Reservoir 14 mi · Carter Lake 14 mi · Hunters Glen Lake 18 mi · Boyd Lake 18 mi · Button Rock Res 18 mi · Windsor Reservoir 22 mi · Standley Lake 22 mi · Gross Reservoir 24 mi · Jim Baker Reservoir 26 mi
See how Union Reservoir stacks up: best largemouth bass lakes in Colorado · best smallmouth bass lakes in Colorado · best walleye lakes in Colorado · best crappie lakes in Colorado
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.