Upper Colorado River Basin above Lees Ferry

Rivers are drawn in proportion to mean annual natural flowThe flow a river would carry without upstream reservoirs, diversions and other water use. Reclamation estimates it by adding those effects back to the measured flow. for water yearsA water year runs from October 1 to September 30 and is named for the year in which it ends: water year (WY) 2020 ran from October 1, 2019 to September 30, 2020. 1906–2020. Select a natural-flow gauge, reservoir or tree-ring siteA stand of long-lived trees whose annual rings record moisture conditions. These sites are being used in an NSF-funded study to reconstruct Colorado River flow at Lees Ferry over the past 2,000 years. for details.

Legend

Mean natural flow, WY 1906–2020
Reservoir storage capacity
Elevation (m)
1000200030004000

Tree-ring chronologies

#ChronologyFirst yearr TotalBest subbasin