Malheur Reservoir
{{Use mdy dates|date=February 2025}}
{{Infobox body of water
| name = Malheur Reservoir
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| location = Malheur, Oregon, United States
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| coordinates = {{coord|44.3649749|-117.6984041|display=inline,title}}{{cite GNIS|1123712|Malheur Reservoir|Jan 16, 2021}}
| type = Lake
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| rivers = Willow Creek
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| area = {{convert|1,282|acre|abbr=on}}
| depth = {{convert|38|ft|abbr=on}}
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| elevation = {{convert|3,365 |ft|abbr=on}}
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| pushpin_map = Oregon#USA
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| pushpin_map_alt = Location of Malheur Reservoir in Oregon, USA.
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Malheur Reservoir is an irrigation lake along Willow Creek in Malheur County in the U.S. state of Oregon. Built by the Orchard Irrigation District in the 1930s, the {{convert|1282|acre|km2|adj=on}} lake can hold about {{convert|49000|acre.ft|m3}} of water, which is used to irrigate about {{convert|2300|acre|ha}} of farmland downstream. Draining a semi-arid rangeland basin of {{convert|254|sqmi|km2}}, the reservoir receives very high concentrations of nutrients and is naturally eutrophic.{{cite book|last = Johnson|first=Daniel M.| title = Atlas of Oregon Lakes| publisher = Oregon State University Press|year = 1985|location=Corvallis|pages = 136–37|isbn=0-87071-343-4|display-authors=etal}}
About 80 percent of the {{convert|12.3|mi|km|adj=on}} shoreline is privately owned, but the lake and part of the shore is open to public use.{{cite book|last= Sheehan| first= Madelynne Diness | title= Fishing in Oregon: The Complete Oregon Fishing Guide|publisher = Flying Pencil Publications|location=Scappoose, Oregon|year = 2005|edition = 10th| pages=279|isbn=0-916473-15-5}} Since the mid-1960s, the reservoir has been stocked with rainbow trout, although fishing conditions have varied with weather cycles, and the reservoir has at times gone dry during drought. During wet cycles, it is capable of producing trout in excess of {{convert|20|in|cm}} long.
The lake is accessible by dirt road, starting either from an intersection with U.S. Route 26, about {{convert|15|mi|km}} to the southwest, near Ironside, or from a different intersection with Route 26, about {{convert|15|mi|km}} to the southeast near Brogan. The lake has a boat ramp on the north shore, and camping is possible in a few places near the ramp. The Malheur County Parks Department maintains the boat ramp as well as gravel parking and a restroom.{{cite web|title = Parks Department|url = http://www.malheurco.org/parks|publisher = Malheur County, Oregon|accessdate = March 7, 2011}}