Upper Cow Lake (Malheur)

Reachcode: 17050108001493 | Area: 1045.0 acres | Shoreline: 10.5 mi | View on Interactive Map

(From Atlas of Oregon Lakes, Johnson et al. 1985).  Upper Cow Lake is one of two quite large lakes located in the Jordan Craters area of southeast Oregon. They were formed when the Cow Creek Valley was choked by a number of geologically recent lava flows. The flows issued from the Jordan Craters which are aligned in a north-south direction a little to the west of Cow Creek. One result of this mode of origin is that the lakes extend into lateral valleys behind the lava dam; hence they have very irregular shorelines. During high water stages water overflows across the basalt to supply a number of other lakes in the lava terrain to the southwest. Inflow to the lakes is from a number of intermittent streams and from seepage through the volcanic terrain. There is a 17-foot difference in water surface elevation between the two lakes when they are full, but during summer months water levels drop considerably. Both are very shallow and are connected by a narrow channel called The Narrows.

Control structures have been constructed at the outlets of both Upper and Lower Cow Lakes and the waters are used for irrigation downstream in the summer. The drainage basin above the lakes is a landscape of sparse vegetation, used mainly for cattle grazing. Much of the area is under the administration of the Bureau of Land Management, interspersed with privately owned lands. Upper Cow Lake is the only one to receive attention from fishermen. It was treated chemically in 1963 and restocked with rainbow trout. Rough fish have returned and inhibit fishing somewhat; but good trout are still taken. The Bureau of Land Management has provided a camp with trailer sites, stores, and supplies, and a boat launch.

Both Upper and Lower Cow Lakes are similar in terms of water quality; both are hypereutrophic. Major ion and phosphorus concentrations are among the highest of any lakes in this survey, whereas transparency values are among the lowest. These lakes have several problems due to their location in an arid, windblown region, and because of their shallow depths. Phytoplankton are abundant (chlorophyl 5.6 ug/l in each lake) as are macrophytes; suspended sediment concentrations are very high; water temperatures are warm; dissolved oxygen is low; and trash fish are overpopulated.