Description of the basin
The Green Lakes Valley (GLV) is U-shaped glacial valley located along the Colorado Front Range with an area of 7 km2 and ranging in elevation from 3250 ~ 4000 m. It is located about six kilometers east of the Continental Divide and just west of large agricultural and urban areas between Fort Collins and Colorado Springs, Colorado within the Silver Lake Watershed, which provides approximately 40% of the water supply for the City of Boulder, Colorado. Public access is prohibited throughout the watershed. The Niwot Ridge Long Term Ecological Research (LTER) site - with permission from the City of Boulder - tracks long-term data on climate, atmospheric chemistry, hydrology and surface water chemistry.
The Green Lakes Valley (GLV) watershed consists of two catchments. The lower catchment has an area of approximately 5 km2, and is subalpine. It includes Lake Albion and Green Lakes 1, 2, and 3. The upper catchment is an alpine ecosystem of about 2 km2 located above treeline, and includes Green Lakes 4 and 5. The two subcatchments are separated by a steep (~100 m tall) waterfall. The upper basin is primarily fed by snowmelt, with minor contribution from glacial run-off including a small rock glacier. Lake sediments are slightly acid and reduced, containing moderate amounts of organic matter, and the median diameters of the sediment particles lie in the medium grained silt range (McNeeley 1983). The dominant erosion process appears to be mass wasting, although additional erosion processes such as hydrostatic pressure may occur (McNeeley 1983). Historically, the upper two lakes were fishless, but due to accidental stocking in 1998, Yellowstone cutthroat trout now inhabit both Green Lakes 4 and 5.
The watershed receives most of its precipitation in the form of winter and spring snowfall. Green Lakes 4 and 5 are ice-free only during the short growing season from late June or early July until early to mid October.