Oregon Lake Inventory:
Clear Lake, Lane County, Oregon

Introduction

Clear Lake is the second in a chain of four lakes located on the central Oregon coast. The chain of lakes; Collard, Clear, Ackerly, and Munsel, lie on the North Florence dunal aquifer, an important drinking water source for the Florence area. The Heceta Water District withdraws directly from Clear Lake, a rare unfiltered drinking water resource. To protect this resource there are no public access roads to the lake and only two residences border the shoreline. Access is available through a one-mile long hike across sand dunes, but recreational use is minimal. Motorboats are allowed. Cutthroat trout and largemouth bass are present.

Figure 1. Lake Watershed

The aquifer is a dominant hydrologic feature of the lake. This is evident through low surface water flows despite and annual average precipitation of nearly eighty inches. Most of the water percolates into the sand and discharges directly into the ocean. (Christensen and Rosenthal 1982). A generalized ground water flow-path is included in figure 2. Surface water inflow comes from Collard Creek to the north and outflow is through Clear Creek into Munsel Lake. Steady year round flows of 1 to 2 cubic feet per second leave the system via Munsel Creek, which flows into the Siuslaw River, and eventually the Pacific Ocean.

Figure 2. Groundwater flow

The lake, bordering sand dunes, and underlying aquifer have a common geologic origin that is typical of the Oregon coast (Cooper 1958). The dunes in this area formed through an accumulation of wind blown sand on a marine terrace that had been warped below sea level. Higher sections of the terrace remain 50 to 150 feet above sea level and can be seen to the north near Newport and to the south near Bandon and Port Orford. The dune sheet that covers the terrace near Florence is permeated with water and forms the North Florence dunal aquifer. The sheet is as much as five miles wide. The lake lies in a trough between the buildup of the dune sheet to the west and the bedrock of the Coast Range foothills to the east.

Watershed Characteristics

The dominant visual features of Clear Lake's watershed are contrasting active sand dunes to the west and lush forests to the east. While forests cover over 40% of the watershed, sand dunes cover less than 15% (table 1). Forests are made up of mixed age coniferous and hardwood species. Water (Clear and Collard Lakes), urban agriculture (residential areas), and non-forested vegetation (marshland) compose the remainder of the watershed. Residential areas and roads are confined mostly to the northern section near Collard Lake. Road density near the lake is very low, but when including the Collard Lake area roads, the density of the entire watershed is similar to others included in this study. Since the eastern side of the lake in bounded by foothills of the Coast Range, the average slope of the watershed is high. The high point of 150 meters is located in the foothills.

Table 1. Lake watershed characteristics

Morphometry

Clear Lake’s shape is nearly oval with no significant arms or bays (figure 3). Most of the shoreline drops quickly to a depth of over four meters. The steepest drop and the deepest point occur on the eastern half of the lake near the foothills of the Coast Range. The northwest and south sections of the lake are the shallowest parts with depths suitable for floating leaved macrophyte growth. The maximum depth observed was 25.5 meters and the average depth is 12.5 meters.

Figure 3. Lake bathymetry

Water Quality

Several water quality parameters were measured in the Clear Lake during the summer of 2001. A summary is provided in table 2. The lake’s trophic state based on Secchi disc depth, chlorophyll a concentration, and total phosphorus concentration ranged from index values of 30 to 39. These values are within the oligotrophic range and compare well with historical data collected by Portland State University and Oregon Department of Environmental Quality (Johnson et al. 1985). A plot of trophic state index values based on these data is provided in figure 4.

Table 2. Water quality

Figure 4. Lake Trophic State

Clear Lake was thermally stratified during visits in July and September at depth of 8.8 and 9.8 meters respectively. Vertical profiles of temperature and other data collected with a water quality probe are plotted below. The entire water column was oxic during the April and July visits, but was anoxic at the deepest section during the September visit. Although anoxic layers are not typical of oligotrophic lakes, this trend does not appear to apply to oligotrophic lakes located in the Oregon coastal dunes.

Macrophyte beds are most extensive in the shallow north and south ends of the lake. The sand, clay and mud sediments in these areas support sparse stands of the floating leaf species Brasenia schreberi, Nymphaea odorata, Potomogeton amplifolius, and Potomogeton gramineus. Submergent vegetation present includes Najas spp., Isoetes spp., and Chara spp.

Clear Lake North, 2001 Data

APRIL 19

JULY 17

SEPTEMBER 17

Resources

Johnson, D. M., R. R. Petersen, D. R. Lycan, J. W. Sweet, M. E. Neuhaus, and A. L. Schaedel. 1985. Atlas of Oregon Lakes. Oregon State University Press. Corvallis, OR

Christensen, R., and B. Rosenthal. 1982. North Florence dunal aquifer study. Lane Council of Governments, Eugene, OR. 153 pp.

Cooper, W. S. 1958. Coastal Sand Dunes of Oregon and Washington. N.Y. Geol. Soc. Am. Memoir 72. New York, NY. 169 pp.