Site Details

descriptions and directions

Cottonwood Marsh photo by Peter Burke

Union Reservoir - Weld County
Aliases: Calkins Lake
Ownership: None Listed
Description: Union Reservoir, marked as Calkins Lake on some maps, is an excellent birding site. Much of the lake can be easily and well surveyed from CR 26 on the south side, and CR 28 on the north. Additionally, there is a park owned by the City of Longmont on the southwestern corner (admission $8 per vehicle and $70 per season, as of 2013), which offers excellent viewing (and some wind protection) for late fall to early spring afternoon birding. As long as there is open water, the lake is often covered with Western and Clark's Grebes, including during summer. It is one of the better reservoirs to check for loons, scoters, Long-tailed Duck, Red-necked Grebe, and Sabine's Gull (in season). Depending on water levels, good numbers of shorebirds and excellent numbers of egrets can be present. The marshes along its edges have attracted wintering Short-eared Owls and Swamp Sparrows. Over the years, Union Reservoir has attracted some major rarities, including Aleutian Cackling Goose, Brant, American Black Duck, Yellow-billed Loon, Brown Pelican, Tricolored Heron, Hud Godwit, Red Phalarope, Ancient Murrelet, BL Kittiwake, Arctic Tern, Gyrfalcon, Black Merlin (Pacific NW subspecies), Sedge Wren, and Sprague's Pipit

Habitat: Pond/Lake/Reservoir, Marsh
Directions: To get to Union Reservoir you will have to get onto County Line Road (Weld CR 1), which can be reached from the north off of CO 66 (4 miles west of I-25, and 2.5 miles east of US-287), or the south off of CO 119 (similar distances as above). To reach the north side of Union, turn off of County Line Road onto CR 28 (0.8 miles south of CO 66, and 2.2 miles north of CO 119). Scan from the various vantage points along this road. Turning right at the intersection of CRs 28 and 3, 1.1 miles from County Line Road, will produce a few more points from which to scan the lake. To get to the south side, turn off of County Line Road onto CR 26 (0.8 miles north of CO 119, 2.2 miles south of CO 66), and scan from the vantage points about 3/4 of a mile down this road.
Other Wildlife:
Other Attractions:

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Latest Union Reservoir Sightings from eBird


CBRC Records from Union Reservoir

SpeciesAccession No.Date(s)
Brant (Black)1999-01910/31/1993 - early November 1993
Tundra Swan2006-164 11/26/2006
American Black Duck2002-10211/30/2002
Red-necked Grebe2-92-11910/23/1992
Hudsonian Godwit2008-030 4/16/2008 - 4/18/2008
Ruddy Turnstone19-93-849/19/1993
Red Knot1953-0015/18/1953
Short-billed Dowitcher19-77-65/23/1976
Jaeger sp.22-77-659/4/1977
Jaeger sp.22-83-612/5/1982 - 12/6/1982
Jaeger sp.22-84-1110/15/1983
Parasitic Jaeger22-77-598/13/1977 - 8/14/1977
Parasitic Jaeger2004-045 9/5/2004
Long-tailed Jaeger22-93-10210/16/1993
Ancient Murrelet1965-00310/14/1965
Black-legged Kittiwake23-76-11811/13/1976 - 11/27/1976
Black-legged Kittiwake23-96-3111/28/1996
Black-legged Kittiwake2002-11212/6/2002
Black-legged Kittiwake2010-159 12/4/2010 - 12/18/2010
Little GullN-23-4511/2/1974 - 11/10/1974
Little Gull23-76-625/22/1976 - 5/27/1976
Little Gull23-77-55/15/1976
Little Gull23-77-606/7/1976
Little Gull23-96-2310/6/1988
Little Gull23-94-3111/3/1994
Little Gull23-95-399/24/1995
Little Gull1999-05310/5/1999
Little Gull2011-174 12/1/2011 - 12/3/2011
Laughing Gull23-76-411/1/1975
Laughing Gull23-76-11210/23/1976
Laughing Gull2002-0455/8/2002 - 5/17/2002
Short-billed Gull23-81-74/28/1981
Short-billed Gull23-92-54/28/1991
Short-billed Gull1997-0373/8/1997
Short-billed Gull1998-06012/5/1998
Short-billed Gull1999-0562/27/1999
Short-billed Gull1999-05711/18/1999 - 11/20/1999
Short-billed Gull1999-05912/31/1999
Great Black-backed Gull23-95-463/8/1995
Arctic Tern23-80-29/11/1979 - 9/12/1979
Arctic Tern1999-07810/5/1999
Arctic Tern2000-16810/6/2000 - 10/7/2000
Arctic Tern2003-1269/13/2003
Arctic Tern2017-033 05/27/2017
Arctic Tern2017-067 10/17/2017
Red-throated Loon2007-089 11/3/2007
Red-throated Loon2007-097 11/17/2007
Red-throated Loon2009-102 10/30/2009 - 11/14/2009
Yellow-billed Loon1-92-5011/9/1991
Brown Pelican3-91-56/23/1991
Tricolored Heron1998-0075/16/1998 - 5/18/1998
Glossy Ibis2010-075 4/4/2010
Red-tailed Hawk (Krider's)2011-024 3/28/2011
Merlin (Black)2013-199 04/23/2013
Sedge Wren2016-014 10/21/2015