Collard Lake is a small sheltered natural lake located on the central Oregon coast. It is the uppermost lake in a chain that includes Clear, Ackerly, and Munsel Lakes (figure 1). These lakes lie on the North Florence dunal aquifer, an important drinking water source for the Florence area. The aquifer is a dominant hydrologic feature of the lakes. 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. A generalized ground water flow-path is included in figure 2. Collard Lake has no discernable surface inflow. Outflow is through Collard Creek to the rest of the chain. 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 1. Lake watershed
The lake, bordering sand dunes, and underlying aquifer have a common geologic origin that is typical of the Oregon coast. The dunes in this area formed through an accumulation of wind blown sand on 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.
Recreational use of Collard Lake is low since nearly all of the shoreline is privately held. One private road provides access to residents. Fishing opportunities for largemouth bass and cutthroat trout exist with permission. Motorboats are prohibited.
Figure 2. Groundwater flow
Collard Lake covers a large percentage of its watershed (table 1). The remainder of the watershed is composed forest, residential area (urban-agriculture) and barren area (sand dunes). A small portion is covered with non-forested vegetation (marshes). Forests consist of both conifer and hardwood species. There are a large percentage of young small trees in the 0-10 inch diameter category. Slopes are steep with high sand dunes to the west and forests and residential areas to the north and east. The high point is in the Coast Range foothills at 150 meters. Road density is high compared to other watersheds included in this study.
Table 1. Lake watershed characteristics
Collard Lake is actually three distinct basins separated by shallow sills (figure 3). The south basin has the deepest point in the system, 17.3 meters. Most of the shoreline mirrors the topography of the surrounding Coast Range foothills and sand dunes with steep drop offs. The mean depth of the lake is 6.4 meters. Shallow sections occur near the sills and in the southernmost lobe of the south basin.
Figure 3. Lake bathymetry
Several water quality parameters were measured in the South Basin of Collard Lake during the summer of 2001. A summary is provided in table 2. Collard Lake’s trophic state based on Secchi disc depth, chlorophyll a concentration, and total phosphorus concentration ranged from index values of 34 to 41. These values are mostly within the oligotrophic range, but close to mesotrophic. Historic data for comparison with these values is scarce, but researchers at Portland State University and the Oregon Department of Environmental Quality sampled the lake two times since 1980. Index values calculated from these and the 2001 data are plotted in figure 4. Tannic acid equivalents, a measure of organic carbon content calculated from color measurements, was higher than the other lakes in the chain.
Collard Lake was thermally stratified during visits in July and September at depth of 4.9 and 6.9 meters respectively. Vertical profiles of temperature and other data collected with a water quality probe are plotted below. Hypolimnetic oxygen depletion was evident during the July and September visits. Although anoxic hypolimnia are not typical of oligotrophic lakes, this trend does not appear to apply to oligotrophic lakes located in the Oregon coastal dunes.
Floating leaved macrophyte species inhabit the shoals between basins and near shore areas. Species present include Brasenia schreberi, Nympheae odorata, and Potomogeton amplifolius. The only submergent species observed was Chara spp.
Collard Lake, 2001 Data