Written by Peter Pearsall/Map showing 1984 flooding at Malheur Refuge by USGS
Located in the northernmost reach of the Great Basin, Malheur Lake in southeastern Oregon is a wildly fluctuating body of water, growing and shrinking throughout history with floods and droughts.
A Lake With No Escape
Malheur Lake is predominantly fed by two rivers. From the north, the Silvies River descends from the Blue Mountains, while from the south, the Donner und Blitzen River carries meltwater and rainfall off the flanks of Steens Mountain. Malheur has no true outlet and is thus a “terminal” lake. When water levels rise high enough (above 1247.5 meters above sea level), overflow spills east into Harney Lake through Mud Lake.
This closed-basin system means that the lake is entirely dependent on inputs from snowmelt, rainfall, and seasonal river flow. With no consistent outflow and a shallow basin floor lying just a meter below the overflow threshold, Malheur Lake is very sensitive to climatic extremes.
From Flood to Drought
From 1978 to 1984, Malheur Lake experienced seven consecutive years of flooding, pushing water levels to the highest in recorded history. The lake swelled, submerging nearly all of its characteristic marsh vegetation and transforming the landscape. But just as suddenly, the hydrologic regime flipped. The following seven years brought severe drought, culminating in 1992 with the lowest water levels seen in 60 years.
Annual changes in mountain snowfall, rainfall, air temperature, and evaporation cause the lake’s surface area to expand and contract dramatically. In especially dry years, vast swaths of the lakebed become cracked, dusty plains. In wet years, those same flats transform into emergent-vegetation marshes expanses teeming with birdlife.
Ancient Basin in a Modern Climate
The lake’s origins trace back to a much wetter time. Malheur, along with Harney and Mud Lakes, are remnants of a vast pluvial lake that once filled much of the Harney Basin during the Pleistocene. As the Ice Age gave way to a warmer and drier climate some 10,000 years ago, water levels dropped, leaving behind a chain of shallow lakes and an ancient outlet to the Malheur River that now lies stranded far above the modern lake level.
Today, Malheur’s average surface area hovers around 18,600 hectares (roughly 46,000 acres), but that figure can vary wildly depending on the year. With a lowest point just 1,246.5 meters above sea level, and past peaks reaching 1,248.5 meters, even small changes in precipitation or snowpack can dramatically alter the lake’s footprint.
A Dynamic Landscape
Malheur Lake is a dynamic, living ecosystem shaped by extremes. It serves as a critical stopover for migratory birds and a rich habitat for wetland species. But its future is deeply tied to climate patterns, making it a bellwether for the impacts of drought, flooding, and long-term environmental change in the American West.
References:
Hydrology of Malheur Lake, Harney County, southeastern Oregon
Recovery of Marsh Vegetation at Malheur Lake Following an Extended Flood
