- Harney County)
(From Atlas of Oregon Lakes, Johnson et al. 1985). Malheur Lake lies in the Malheur/Harney Lake Basin in southeastern Oregon. It represents a remnant of a much larger waterbody that existed during the Pleistocene Epoch when precipitation was greater and evaporation less. At its highest level this "pluvial" lake is estimated to have been 900 square miles in surface area, with a maximum depth of 35 feet (Phillips and Van Denburgh 1971). It overflowed eastward into the Snake River via the Malheur River. Drainage was first through a channel near Princeton, and later through a gap at Crane when Pleistocene lavas blocked the former channel (Baldwin 1976). About 10,000 years ago warmer and drier conditions caused the pluvial lake to shrink, and the water no longer had an outlet to the sea. Much of this former lake bottom is now brush-covered desert and seasonally flooded grass-sedge meadowland, with Malheur and Harney Lakes existing as remnants of the former Pleistocene lake.
The first written information about Malheur and Harney Lakes is in Peter Skene Ogden's journal of his third Snake River expedition. On November 1, 1826, his party first sighted the lakes. Ogden did not name them but he did refer to the ridge or dike that separated the large freshwater lake from the salt water to the west. In 1859 an infantry division under Captain H. D. Wallen, while on an expedition from The Dalles to Great Salt Lake, reached the salt water and named it Lake Harney. The horses would not drink the alkaline water and stampeded over the dike eastward to what is now Malheur Lake. Wallen tnereupon named the fresh water body Lake Stampede, a name that has not prevailed. Malheur Lake was eventually named for Malheur River, the name used by Ogden in 1826 (River au Malheur = "unfortunate river") because of property and furs having been hid there and then discovered and stolen by natives. It is not known when the name was first applied to the lake (McArthur 1974).
Malheur Lake is, in effect, a freshwater marsh, one of the largest in the country. It has long been one of the most productive waterfowl breeding areas in the United States, and is a vital migration habitat for birds on the Pacific Flyway. In 1908 President Theodore Roosevelt dedicated the area as a bird refuge, and the Malheur National Wildlife Refuge now comprises nearly 160,000 areas of open water, vast tule swamps, wild meadows, and wooded areas. It is a remarkable area, and well over 200 different species of birds have been found on and adjacent to the Malheur Refuge.
The hydrology of the Malheur Lake Basin has a direct and powerful effect on the size and on the limnological character of the lake. Historically, it has been dry during extreme droughts; for example it was completely dry in 1934 and nearly dry in 1926, 1931-33, and 1961-62 (Phillips and Van Denburgh 1971). At high-water levels the surface area exceeds 50,000 acres, with a maximum depth of about 6 feet. In the early 1980s a sequence of wet winters caused extensive flooding in the basin, with the water of Malheur and Harney Lakes extending well past their "normal" shorelines. At a water surface elevation of 4091.5 feet (maximum depth = 2.5 feet), water flows through The Narrows, a winding weed-grown channel, to Mud Lake. At higher levels it overflows the dike into Harney Lake, the sump, or end point, of this large naturally-closed basin. Harney Lake thus has become very alkaline, losing water only via evaporation, while Malheur Lake is periodically freshened.
The topographic drainage basin to Malheur Lake is 3083 square miles, of which approximately 30 percent is non-contributing. Inflow of water is from four principal sources -- surface runoff from the Silvies River and the Donner und Blitzen River, Sodhouse Spring on the periphery of the lake, and direct precipitation on the lake surface (Hubbard 1975). The Donner und Blitzen River, draining an area of 760 square miles, is the largest contributor. It is supplied primarily by snowmelt from Steens Mountain., but its flow into Malheur Lake is substantially reduced by upstream diversions for irrigation. The Silvies River has a drainage area of approximately 1200 square miles, and during spring flooding water enters the lake through both the East Fork and the West Fork channels and at many points between the two channels. The river contributes less inflow to the lake than does the Donner und Blitzen because of the large quantity of water diverted for irrigation. Inflow from all streams and springs has been estimated to average about 100,000 acre-feet per year (Phillips and Van Denburgh 1971). Since the capacity of the lake basin at the overflow elevation is only slightly more than this, about 120,000 acre-feet, overflow occurs frequently.
Water chemistry in Malheur Lake is variable and is strongly influenced by hydrological events. The lake as a whole becomes appreciably more saline during dry periods and more dilute during wet periods, because of solute depletion by overflow. The lake may be divided into three distinct sub-basins which differ substantially in ecological character (Duebbert 1969). The central basin, east of Graves Point and west of Cole Island, is the deepest and receives the flow ofthe Donner und Blitzen and Silvies Rivers, making it relatively less saline. The dominant emergent macrophyte is hard stem bull rush (Scirpus sp.) and the commonest submerged macrophyte is water milfoil (Myriophyllum exalbescens). This sub-basin is heavily colonized by herons, egrets, grebes, and terns during nesting season. The eastern sub-basin lies east of Cole Island dike, but there is no exit so that evaporation and lack of flushing cause the water to become considerably more saline. An exception is the concentration of calcium which sometimes is lowest in the eastern basin where biogenic precipitation of calcite removes calcium. In this sub-basin, there is less growth of emergent macrophytes but extensive growth of the submerged macrophyte Sago pondweed (Potamogeton pectinatus), an important food source to ducks. The western sub-basin lies west of Graves Point and consists of a complex of interconnected channels and ponds. There is considerable growth of emergent macrophytes; the most important submerged macrophyte is Sago pondweed. As noted, during wet years water rises in Malheur Lake until it overflows from the western basin through Mud Lake and on into Harney Lake. Therefore, during wet years, the western basin of Malheur Lake is also flushed with fresh water.
Primary production in Malheur Lake is very high and the lake is therefore classified as eutrophic. The primary production is dominated by the growth of macrophytes with relatively little contribution by phytoplankton. The unfortunate introduction of carp into the basin, probably in the early 1920s, is thought to have disturbed the ecology of the lake basin. Carp have sometimes reached enormous population densities, and their bottom scouring activities cause the resuspension of bottom sediment. Submerged macrophytes suffer because of the alteration of light caused by the resuspended sediment. Efforts to eliminate the carp with protenone have been unsuccessful.