When the current state highway numbering sytem was first posted in January 1964, SR 151 started at Jct US 2 at Orondo and headed north along the east side of the Columbia River to the Beebe area. SR 151 crossed the Columbia to the Chelan Falls area, then headed uphill to Jct US 97 (now Alt US 97) on the east side of Chelan. A spur left the SR 151 mainline a couple of miles before the SR 151 mainline/US 97 Jct. This spur headed north to connect with US 97, providing a shortcut for traffic headed north toward the Okanogan Valley.
Around 1985, a newer SR 151 spur alignment was built heading north from the Chelan Falls area to Jct US 97. This new alignment completed the so-called water grade route between Wenatchee and the Okanogan Valley. The idea of switching US 97 to the water grade route had been discussed since the beginning of the US route numbering system in 1926. In fact, maps from the late 1920s and early 1930s had shown the route along the west side of the Columbia as Temporary US 97. The west side route had been the better route before completion of the water grade route and the temporary designation had eventually been dropped from the west side route. A private toll suspension bridge was built across the Columbia in the Chalan Falls-Beebe area. In 1937, the route that was to become SR 151 had been downgraded from Primary State Highway 10 to Secondary State Highway 10D.
In 1963, completion of a new state owned bridge across the Columbia between Beebe and Chelan Falls signalled that plans for completion of the water grade route were still alive. In 1987, a few years after the missing link in the water grade route was completed, US 97 was swithced from the west side route from the Wenatchee area to the Chelan area to the watergrade route. The SR 151 designation disappeared, replaced by US 97. SR 151 from Chelan Falls to Chaelan became an eastern extension of SR 150.
Primary State Hwys Secondary State Hwys