Union Reservoir Fishing
A 751-acre Colorado reservoir in Weld County at 4,958 feet.
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Union Reservoir: setting, size and how to reach it
Union Reservoir spreads over roughly 751 acres of Weld County, by its mapped outline. Its surface sits near 4,958 feet above sea level. Union Reservoir and Park manages the ground around it. Plan supplies in Longmont, near 4 miles from the shore. In CPW terms it is a Northeast Region water.
CPW records black bullhead, black crappie, bluegill, channel catfish, common carp and largemouth bass in this water. The boating entry reads Motor boats (gasoline). CPW calls access easy; pressure runs medium. For hard water, CPW has ice fishing listed as no.
CPW Fishing Atlas 2025 layers (waterbody outline, Boatable Waters, fishing locations), Census places, retrieved October 25, 2026.
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Tap a fish to open its Colorado page, with limits and records, from Union Reservoir.
CPW Boatable Waters species field, CPW state records and stocking report, retrieved October 25, 2026.
Launching a boat at Union Reservoir
CPW maps no boat ramp right on Union Reservoir; the nearest ones follow.
Atlas fishing locations at Union Reservoir
- Union Reservoir fishing access near Longmont, Union Reservoir and Park 2accessible fishing area
- Union Reservoir fishing access near Longmont, Union Reservoir and Parkaccessible pier, easy access, stocked: warmwater, 4,958 ft
When the Union Reservoir ramp is crowded
- Saint Vrain State Park on St. Vrain State Park Blue HeronSt. Vrain State Park Blue Heron, 3 miles southeast
- Lonetree Reservoir boat ramp near LovelandLonetree Reservoir, 12 miles northwest
- Boulder City Reservoir boat rampBoulder City Reservoir, 12 miles southwest
- Lon Hagler boat ramp near LovelandLon Hagler Reservoir, 14 miles northwest
- Marina on Carter ReservoirCarter Reservoir, 15 miles northwest
- Boedecker Reservoir boat rampBoedecker Reservoir, 15 miles north
CPW boat ramp and Fishing Atlas fishing location layers, retrieved October 25, 2026.
Water supply gauge at Union Reservoir
Cooperative SDR Program of CDWR & NCWCD storage telemetry for Union Reservoir (station UNIRESCO), recorded October 25, 2026; retrieved October 25, 2026. Provisional data from CDSS.
Colorado reservoirs rise with runoff and drop through irrigation season, so ramps at Union Reservoir can change by the week.
Harvest rules for Union Reservoir
| Species | Bag and possession | Season |
|---|---|---|
| Trout, arctic char, grayling, salmon and whitefish (not kokanee) | Daily bag 4, possession 8, in aggregate | Open all year, day and night, unless a special regulation says otherwise |
| Brook trout 8 inches or less (bonus) | Daily bag 10, possession 10 | Open all year, day and night, unless a special regulation says otherwise |
| Kokanee salmon | Daily bag 10, possession 10 | Open all year, day and night, unless a special regulation says otherwise |
| Walleye, saugeye and sauger | Daily bag 5, possession 5, in aggregate | Open all year, day and night, unless a special regulation says otherwise |
| Largemouth, smallmouth and spotted bass | Daily bag 5, possession 5, in aggregate | Open all year, day and night, unless a special regulation says otherwise |
| White bass, striped bass and wiper | Daily bag 10, possession 10, in aggregate | Open all year, day and night, unless a special regulation says otherwise |
| Channel, flathead and blue catfish | Daily bag 10, possession 10, in aggregate | Open all year, day and night, unless a special regulation says otherwise |
| White and black crappie | Daily bag 20, possession 20, in aggregate | Open all year, day and night, unless a special regulation says otherwise |
| Bluegill and other sunfish | Daily bag 20, possession 20, in aggregate | Open all year, day and night, unless a special regulation says otherwise |
| Yellow perch | Daily bag 20, possession 20 | Open all year, day and night, unless a special regulation says otherwise |
| Tiger muskie | Daily bag 1, possession 1; at least 36 inches long | Open all year, day and night, unless a special regulation says otherwise |
| Northern pike and bullhead | No bag or possession limit | Open all year, day and night, unless a special regulation says otherwise |
Drainage matters for walleye, wiper and perch limits; Union Reservoir sits east of the Continental Divide. Outside any special regulation, these statewide numbers govern Union Reservoir.
Brochure rules for Union Reservoir
| Water as printed | Rule | Brochure |
|---|---|---|
| Union Reservoir (Calkins Lake) | Min. size for wiper is 15 inches long. Bag and possession limit for wiper is 5. | p. 38 |
Special regulations as printed in the 2026 Colorado Fishing brochure (CPW, season March 1, 2026 to March 31, 2027), pp. 11 to 39, checked against CPW Chapter W-1 (as approved 13 November 2025); retrieved October 2026.
Statewide bag and possession chart, 2026 Colorado Fishing brochure (CPW, season March 1, 2026 to March 31, 2027), p. 10, retrieved October 25, 2026.
Trout stocking dates at Union Reservoir
CPW put Union Reservoir on its weekly catchable trout report 3 listings; the most recent listing is dated June 12, 2026.
| Report date | What CPW lists |
|---|---|
| June 12, 2026 | catchable trout, CPW Northeast Region |
| March 14, 2025 | catchable trout, CPW Northeast Region |
| March 5, 2024 | catchable trout, CPW Northeast Region |
CPW Fish Stocking Report (catchable trout of about 10 inches; the date is when CPW added the water to its weekly list), 2024 to October 2026, retrieved October 25, 2026. Colorado stocking.
How Union Reservoir measures up to the water around it
| Lake | Distance | Acres | Elevation ft | Boat ramps | On the trout report |
|---|---|---|---|---|---|
| Union Reservoir | 751 | 4,958 | 0 | yes | |
| St. Vrain State Park Blue Heron | 3 miles southeast | 80 | 4,844 | 1 | |
| St. Vrain State Park Mallard | 3 miles east | 7 | 4,835 | 0 | yes |
| St. Vrain State Park Pintail Pond | 3 miles southeast | 4 | 4,843 | 0 | yes |
| St. Vrain State Park Pelican | 3 miles east | 42 | 4,833 | 0 | yes |
| St. Vrain State Park Coot Pond | 3 miles southeast | 7 | 4,843 | 0 | yes |
CPW Fishing Atlas, ramp layer and stocking report, retrieved October 25, 2026.
The ground surrounding Union Reservoir
Other reservoirs within a drive of Union Reservoir
- St. Vrain State Park Blue Heron3 miles southeast
- St. Vrain State Park Mallard3 miles east
- St. Vrain State Park Pintail Pond3 miles southeast
- St. Vrain State Park Pelican3 miles east
- St. Vrain State Park Coot Pond3 miles southeast
Where to buy line and lures near Union Reservoir
- Angles Sportssporting goods store, Longmont, 4 miles
- Laughing Grizzly Fly Shopfly shop, Longmont, 4 miles
- Woods and Water Outfittersbait and tackle shop, Longmont, 4 miles
- Backcut Fly Shopfly shop, Berthoud, 9 miles
- Sarabella Fishingbait and tackle shop, Erie, 9 miles
- Bennetts Tacklebait and tackle shop, Berthoud, 9 miles
Outfitters who fish Union Reservoir
- Anglers Edgefishing guide, Windsor
- Kindred Anglers LLCfishing guide, Dacono
- The Reel Mission Fishin' Adventuresfishing guide, Greeley
- Estes Park Fly Fishing LLCfly fishing guide, Greeley
Beds and gas close to Union Reservoir
- Longmont4 miles
- Mead4 miles
- Firestone5 miles
County guides that cover Union Reservoir
- Weld Countyseat: Greeley
Piscifun tackle sized for Union Reservoir
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Reservoirs and creeks near Union Reservoir in photos
Photo: KimonBerlin, CC BY-SA 2.0
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Photo: Akijione, CC BY-SA 3.0
Photo: G. Lamar, CC BY 2.0
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Photo: SOTMUS, CC BY-SA 4.0
Before you drive to Union Reservoir, read these
Where in Colorado is Union Reservoir?
CPW maps it in Weld County, CPW Northeast Region, about 4 miles from Longmont.
How many acres does Union Reservoir cover on CPW maps?
Close to 751 acres by the CPW outline, at about 4,958 feet.
Which ramp do boaters back down at Union Reservoir?
CPW maps none here; try a neighbor.
Which gamefish does CPW tie to Union Reservoir?
CPW lists black bullhead, black crappie, bluegill, channel catfish, common carp, largemouth bass and rainbow trout.
Does the brochure print a special rule for Union Reservoir?
Trout, arctic char, grayling, salmon and whitefish (not kokanee): Daily bag 4, possession 8, in aggregate. Extra rules from the brochure apply; they are above.
Can an out-of-state visitor fish Union Reservoir on a short license?
Colorado sells no separate trout stamp; a CPW fishing license covers trout ($44.87 for adult residents, $124.01 for nonresidents), and anglers 16 and older need one.
When did CPW last list Union Reservoir for trout?
The report carries 3 listings on the CPW catchable trout report (1 in 2026, 1 in 2025, 1 in 2024); latest June 12, 2026.
Where can I pick up bait on the way to Union Reservoir?
Closest on our list: Angles Sports, 4 miles.
What does the latest reading at Union Reservoir show?
See Colorado Division of Water Resources telemetry in the band above.
Can I drill holes at Union Reservoir?
CPW lists ice fishing listed as no; no ice is ever certified safe.
Give Union Reservoir an early start
Buy the CPW license online before you leave.