- Jackson County)
(From Atlas of Oregon Lakes, Johnson et al. 1985). Willow Lake is a popular southern Oregon reservoir which stores the waters of Willow Creek, a tributary of the South Fork of Big Butte Creek. It is commonly known as Willow Creek Reservoir and this name appears routinely on maps. The 52-foot high, earthfill dam was completed in 1952 by the Medford Water Commission to store water as part of their municipal water system. Other uses are for irrigation and recreation. The contributing drainage basin is primarily within the Rogue River National Forest and drains the west slopes of Mt. McLoughlin. However, there are many sections of privately owned land within the broader National Forest boundaries. The lake itself is on county land, which has been developed by Jackson County as the Willow Lake Recreation Area. It includes facilities for camping and picnicking as well as a paved boat ramp. A small, private resort is also located on the shore. Willow Lake is heavily fished; kokanee were stocked about 1960 and have produced very well. Rainbow and cutthroat trout are also found, although in lesser numbers.
Water in Willow Lake has low concentrations of major ions, and the alkalinity and conductivity are less than average for reservoirs in the Rogue Basin. Concentrations of phosphorus and chlorophyl are moderate, and water transparency is average, indications of a mesotrophic lake. However, Willow Lake is not without serious water quality problems. It is a relatively shallow water body, especially in the southern arms where Willow Creek and Bieberstedt Creek enter, and it varies considerably in depth and area throughout the year because of irrigation withdrawals. Macrophytes are observed growing excessively in these shallow areas. Algal blooms are not uncommon and they give the water a greenish hue. A past history of sewage discharge into the lake has contributed to water quality problems. In fact, Willow Lake is the location of what was probably the first recorded case, in Oregon, of mass poisoning of swimmers by blue-green algae. Sewage from the campground and the small resort is treated in a small treatment structure. Presumably, the treated effluent eventually enters the water, as evidenced by the fact that oxygen depletion is sometimes pronounced below a depth of 20 feet (6 meters). On the sample date of 7/15/82 a bloom of Gloeotrichia echinulata, a blue-green alga, was dominant. Other blue-greens, Aphanizomenon flos-aquae and Anabaena sp. were also observed. All these species are distinct indicators of enriched conditions. The combination of parameters suggests that a classification of eutrophic is appropriate.
McHugh (1979) has proposed methods to alleviate this problem of enrichment. The effluent could be piped past the lake and released below the dam or, as is now done at Emigrant Lake, accumulated and periodically sprayed on adjacent forested areas or dry hillsides. Another suggestion is to take advantage of the seasonal drawdown and deepen the reservoir near the shoreline. Such deepening would limit the now excessive growth of macrophytes in shallow water and, by reducing total surface area, would decrease evaporative loss and water warming.