The Okanagan–Similkameen is a small and arid drainage region located in southern British Columbia near Lake Okanagan, Lake Osoyoos and the Similkameen River. In 2011, 88.2% of its total area was natural and semi-natural area, 9.0% was natural land for pasture and arable land and 2.8% was built-up area.
The population was 327,548 in 2011, with a population density of 21.8 persons/km2, the third highest in the country. Population was up 176% compared to 118,507 in 1971.
Surface freshwater intake from drinking water plants, irrigation and manufacturing was 148.3 million m3 in 2013.
The average annual water yield was 4.3 km3 over the period of 1971 to 2013 —the second lowest in the country. The water yield per unit area was 0.27 m3/m2, compared to 0.35 m3/m2 at the Canada level. Monthly water flows peak in May. The monthly variability index was the third highest in the country, indicating the monthly flows can vary widely from year to year.