Woahink Lake is a large, deep, clear lake located about three miles inland from the central Oregon coast, directly south of the city of Florence. The lake is popular for boating, swimming and fishing by both residents and visitors alike. Fish species present include yellow perch, largemouth bass, rainbow trout, cutthroat trout, kokanee, and coho salmon. Woahink Lake’s primary recreational access point is through Jessie C. Honeyman State Park. This 522-acre park contains developed recreational areas and undeveloped natural areas. A nationally endangered species of pitcher plant (Darlingtonia californica) grows in the bog areas within the park. The park covers about 15 percent of the lake’s shoreline. Much of the remainder consists of private lakeside residences.
The lake basin owes its origin to the periods of submergence and emergence of the coastal zone that accompanied the latter stages of the Pleistocene Epoch (Cooper 1958). During periods of submergence, coastal streams were inundated by the higher sea level. Subsequent migration of sand dunes across the mouths of the streams as ocean levels decreased created impoundments. The current water surface of Woahink Lake is 38 feet above mean sea level, and the bottom at its deepest point is 74 feet deep, or about 36 feet below sea level, the lowest of any of the sand-dune dammed lakes on the Oregon coast. Tributaries feed three large arms from the north and east; the longest of the three is only about three miles in length. The lake empties southward into adjacent Siltcoos Lake through the Woahink Creek outlet.
Woahink Lake’s watershed is 1784 hectares with 16.8 percent covered by the lake itself (table 1). More than half of the watershed is covered with conifer and hardwood forests. The eastern shoreline of the lake abuts the forested foothills of the Coast Range. The remainder consists of residential areas (urban-agriculture in table 1), non-forested vegetation, and a small percentage of sand dunes and urban areas. The sand dunes in the watershed are the edge of a large active dune area to the southwest within the Oregon Dunes National Recreation Area. Urban areas within the watershed are located along highway 101, a major north south arterial. Road density is similar to that of other watersheds near the central Oregon coast. Average precipitation, nearly 80 inches per year, is typical of the Oregon coast area.
Woahink Lake exhibits the characteristic dendritic, or branching, pattern of an impounded water body (figure 3). The southern half of the lake is much deeper than the northern half with large areas with depths greater than fifteen meters. The deepest point measured in the lake during the summer of 2000 was 22.8 meters. The northern half consists of three relatively shallow arms with extensive areas less than ten meters deep. The mean depth for the entire lake is 11.4 meters.
Several water quality parameters were measured in Woahink Lake during the summer of 2001. A summary is provided in table 2. Woahink 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.
Woahink Lake is a monomictic lake with temperature stratification during the summer months and complete mixing during the winter. In April of 2001 the lake was mixed while in July and September the lake was stratified at depths of 8.8 and 9.8 meters respectively. Vertical profiles of temperature and other data collected with a water quality probe are plotted below. Hypolimnetic oxygen depletion at the very bottom of the water column was evident during the September visit. At least some degree of anoxic hypolimnia appears to be typical of central Oregon coast dune lakes.
Macrophytes are not a problem here as they are in so many other coastal lakes; they are present in low numbers and in the shallow ends of the arms. Parrotfeather (Myriophyllum aquaticum) and Elodea canadensis are two non-native invasive species that are present. Other species present include Brasenia shcreberi, Nuphar lutem, Nymphaea odorata, Valisineria americana, Utricularia vulgaris, Utricularia spp., Potamogeton spp., Myriophyllum spp., Scirpus spp., Isoetes spp., Najas spp., Chara spp., and Juncus supiniformis.
Although the water quality of Woahink Lake appears to be in good shape, there are concerns for the future. Further development of the watershed and the introduction of non-native invasive species pose significant threats. Control of these threats is important for many reasons, not the least of which is that untreated water has been pumped from the lake for drinking and domestic purposes. Any degradation in water quality would impair this use, and would also impair recreational enjoyment of the lake.
Woahink Lake, 2001 Data