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Watersheds

Watersheds

Diamond Lake Watershed

Key Statistics

Size (acres) 42,898
Percent public ownership 100
Miles of anadromous salmonid streams 0
Highest elevation (feet) 9,182
Lowest elevation (feet) 5,180

Location and Size

The Diamond Lake fifth-field watershed is located on the far eastern edge of the Umpqua Basin. The watershed is 42,898 acres and includes Diamond Lake itself and the north end of Crater Lake National Park. The Diamond Lake Watershed stretches a maximum of 15 miles north to south and 9 miles east to west.

Landscape and Features

The Diamond Lake Watershed is characterized by gentle to moderate slopes and low relief topography. The exception is the jagged Mount Thielsen, "the Lightning Rod of the Cascades," on the northeastern edge of the watershed at the crest of the Cascade Mountains. Watershed elevations range from 9,182 feet at Mount Thielsen to 5,180 feet where 3,031-acre Diamond Lake empties into Lake Creek. Other high-elevation areas include Mount Bailey (8,368'), Llao Rock (8,049'), and several volcanic cinder cones throughout the watershed. With the exception of some headwater streams in the watershed's northeast corner, most streams within the watershed are of fairly low gradient.

This watershed boasts many interesting geological features, including Mount Thielsen and several other relatively young volcanoes. Evidence suggests that glacial erosion carved Diamond Lake itself, with glacial deposits forming the boundary between the Diamond Lake Watershed and the Clearwater Watershed to the west. The eruption of Mount Mazama, with the subsequent formation of Crater Lake, about 7,000 years ago spewed pumice and ash over a widespread area of the watershed, including the expansive Pumice Desert at the south end of the watershed.

All of the residents in the watershed live around the north and west sides of Diamond Lake itself, where there are many vacation and rental homes and cabins. There are no incorporated cities within the watershed. The major roads within the watershed include State Highway 138 (the North Umpqua Highway), State Highway 230, and the north entrance road to Crater Lake National Park.

The vast majority of the land base in the Diamond Lake Watershed is used for public forestry purposes. Much of the watershed is comprised of Diamond Lake (occupying 7 percent of the watershed) and the resort and recreational facilities surrounding it. Land ownership is solely federal, with administration by the U.S. Forest Service's Umpqua National Forest (northern 61% of watershed) and the National Park Service's Crater Lake National Park (39% of watershed). The Forest Service-administered portion is comprised primarily of the Oregon Cascades Recreation Area, with smaller portions of the Mount Thielsen Wilderness on the east side and matrix areas on the south side. Matrix lands are those available for timber management at varying levels.

Current Conditions

Prior to 1910, the Diamond Lake Watershed did not have a resident fish population. Diamond Lake is shallow, and tributary stream temperatures are less-than-optimal for fish. Diamond Lake is stocked annually to maintain a rainbow trout population. The tributary streams have few resident fish.

Tui chub and golden shiner, most likely introduced as bait fish, are numerous in Diamond Lake. Diamond Lake is being drawn down to allow rotenone treatment of tui chub and other undesirable fish in September 2006. The treatment may have indirect effects on Lake Creek, Lemolo Reservoir, and the North Umpqua River, all located downstream of Diamond Lake and outside the watershed.

Diamond Lake, the dominant water body in the Diamond Lake Watershed, is on the final 2002 ODEQ 303(d) list for summer pH and aquatic weeds and algae.

Stream channel stability is moderate to high, with little significant slope failure or mass movement and minimal amounts of stream bank erosion (1996 and 1997 stream surveys). Large woody debris in stream channels is not in deficit, having moderate frequency in all steam types. Riparian areas remain intact.

Sources

ODEQ 303(d) list: http://www.deq.state.or.us/wq/assessment/rpt02/gis02.zip. Accessed on-line on January 13, 2006.

USFS Watershed Analysis: Lemolo and Diamond Lakes Watershed Analysis. Diamond Lake Ranger District, Umpqua National Forest, 1998.

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