varying flood control requirements in the Columbia Basin. Water releases from Dworshak are also timed to benefit Pacific salmon and steelhead migration in the Clearwater, Snake and Columbia Rivers. During late summer through the fall, large volumes of cold water are released through the dam's low level outlets to help cool water in downstream rivers, creating more suitable temperatures for these fish species. These environmental or "flow augmentation" releases significantly increase water levels during the late summer, with up to being released through the dam in August and in September. The temperature of the released water generally varies from . Tourism and economy One of the major benefits touted by proponents of the Dworshak Dam was that it would provide recreation and associated economic benefits to local residents. The annual visitation to Dworshak is estimated at between 110,000 and 140,000 people, mostly during the summer high water months. Recreational activities include boating, water-skiing, camping, fishing, hiking and hunting; six boat ramps lie adjacent to the reservoir. Idaho's Dworshak State Park is located on Dworshak Reservoir about north of the dam. The uppermost arm of the reservoir extends into the Clearwater National Forest. A regional visitor center is located at Dworshak Dam, and tours are available of the dam itself. However, the large annual drawdown of the reservoir causes boat ramps and marinas to be out of reach for months each year and an unsightly "bathtub ring" to be visible along the shoreline. A study by the University of Idaho calculated that this mode of operation causes the loss of between $4.5–5.9 million of tourism revenues each year. The creation of a slackwater pool along of the North Fork formerly assisted logging operations in the region, although the scale of the lumber industry has decreased significantly since the 20th century. About 81 million board feet were transported on Dworshak Reservoir between 1988 and 1991; however, logs have not been barged on the lake since 1991. This is in part because of the implementation of a late-summer flow augmentation scheme that requires greater drawdowns of the reservoir, putting log-handling facilities well above the water level, and also because of the development of backcountry logging roads that allow more efficient transport by truck. It has been suggested that some of Dworshak's flood control space be shifted to Grand Coulee Dam in northern Washington to provide increased water for flow augmentation; this would carry