Okanagan Lake is situated in south central British Columbia. It has acatchment area of over 6,000 km2 and is the largest of the five main and interconnected lakes in the Okanagan valley. The Okanagan valley is U-shaped with mountains rising on both sides to 1,000-2,500 m.

Okanagan Lake in general is a deep, oligotrophic water body with two shallower reaches with poorer water circulation, higher nutrient levels, and greater plankton abundance. The lake in profile is composed of three basins, a large north basin, a mid basin and a southern basin. It is jointed to Kalamalka Lake in the north by Vernon Creek and at the south end to Skaha Lake by the Okanagan River. This river flows south through Skaha Lake, Vaseaux Lake and Osoyoos Lake; it joins the Columbia River near Brewster, Washington.

Several hundred meters of unconsolidated materials deposited during the Pleistocene epoch line the valley bottom. These materials probably resulted from glacial outwash, direct glaciation, and lacustrine fluvial sedimentation. Notable characteristics of the valley, particularly at the south end, are the terraces which were formed as the lowering of postglacial lake levels were repeatedly arrested. These fertile benches have been used extensively for horticulture, principally fruit trees and grape growing.

Three major population centres are located along lake Okanagan shores: Vernon at the north end, Kelowna at the mid point and Penticton at the south end (Penticton's sewage effluent is discharged to the outflow of Okanagan Lake). The major industrial development in the valley is associated with agriculture and forestry. As well, a large copper deposit has been developed in the drainage basin. Tourism is also a major economic factor in the local economy. These facts coupled with the arid nature of the region have resulted in a very high economic value being given to water quality and quantity. This is reflected by the number of studies conducted on the Okanagan lakes in recent history. Federal-provincial studies in 1969-1974 and 1977-1982 provided the first basic technical information on all the valley lakes and tracked water quality following sewage treatment improvements at Vernon and Penticton. Water quality improvement in the central basin of the lake is expected now, so that the city of Kelowna has instituted tertiary treatment (1).