The Sandy River is a tributary of the Columbia River in northwestern Oregon in the United States. The Sandy joins the Columbia about upstream of Portland.
thumb|Sandy River headwaters
Course
Issuing from Reid Glacier on the southwest flanks of Mount Hood in the Cascade Range, the Sandy River flows generally west and then north for through Clackamas County and Multnomah County to the Columbia River at Troutdale. In its first , the Sandy River flows across Old Maid Flat, north of Zigzag Mountain in the Mount Hood Wilderness of the Mount Hood National Forest. In this initial stretch near the headwaters, it receives Rushing Water Creek from the left, Muddy Fork from the right, then Lost Creek and Horseshoe Creek from the left, and crosses under Lolo Pass Road just before receiving Clear Creek from the right. At about from the mouth, the Zigzag River enters from the left near the unincorporated community of Zigzag. From here the river runs roughly parallel to U.S. Route 26, which is on its left for about the next . Just below Zigzag, the Sandy River passes the unincorporated community of Wemme on the left.
At about from the mouth, the river receives Hackett Creek from the right, passes the unincorporated community of Brightwood shortly thereafter, and receives North Boulder Creek from the right. Barlow Trail County Park and remnants of the Barlow Road lie to the right along this stretch of the river. Between and from the mouth, the Salmon River enters from the left. Roughly later, Wildcat Creek enters from the left and then Alder Creek and Whiskey Creek, also from the left. The river passes the Marmot gauging station operated by the United States Geological Survey (USGS) in cooperation with Portland General Electric at river mile (RM) 29.8 (river kilometer (RK) 48.0). The unincorporated community of Marmot lies to the right of the river on a ridge—the Devil's Backbone—separating the Sandy River from the Little Sandy River to the north.
About below the Marmot gauge, the river receives Badger Creek from the left. It passes under Ten Eyck Road about from the mouth, flowing by the city of Sandy on the left, shortly thereafter and receiving Cedar Creek, home of the Sandy Fish Hatchery, from the left. At about from the mouth, the river turns away from Highway 26 and flows generally north-northwest for the rest of its course. About further downstream, the river passes Dodge Park on the right, receives the Bull Run River from the right and passes a second USGS gauge at RM 18.4 (RK 29.6). Shortly thereafter, Walker Creek enters from the right. Between and from the mouth, the Sandy River enters Multnomah County, curves back into Clackamas County, and re-enters Multnomah County. About further downstream, Bear Creek enters from the left, and the river flows around Indian John Island. On November 3, 1805, William Clark wrote: "I arrived at the entrance of a river which appeared to Scatter over a Sand bar, the bottom of which I could See quite across and did not appear to be 4 Inches deep in any part; I attempted to wade this Stream and to my astonishment found the bottom a quick Sand, and impassable ...".
One of the first documented visits by European-Americans to the upper Sandy River basin occurred in 1838, when Daniel Lee, the nephew of missionary Jason Lee, used the Indian trail over Lolo Pass to drive cattle from a Methodist mission in the Willamette Valley to a mission in Wascopam. Other pioneers later used the trail to drive livestock over the mountains. The first wagons came over the Cascades in 1840, and in 1843 the great east–west migration of settlers to the Oregon Territory began. The Barlow Road, along the Indian trail leading west from the Lolo Trail, opened in 1846 and became popular with new settlers. A branch of this road followed the Devil's Backbone between the Sandy and the Little Sandy watersheds. When in 2008 they demolished Little Sandy Dam, Roslyn Lake ceased to exist. After Marmot Dam was gone, the Sandy flowed freely for the first time since 1912, With the Marmot Dam removal and other habitat restoration in the Sandy River Basin Salmon, Steelhead, and Pacific lamprey are making a comeback. The Lower Salmon River upstream of the former Marmot Dam in recent years has undergone extensive riparian and river restoration. Engineered log jams and the opening of former side channels blocked by the Army Corps of Engineers since the devastating 1964 floods have taken place.
Recreation
In 1988, Congress added about of the Sandy to the National Wild and Scenic Rivers System. The designation applies to two separate segments. One, administered by the U.S. Forest Service, covers from the headwaters to the Mount Hood National Forest boundary. The other, administered by the Bureau of Land Management, covers between Dodge Park and Dabney Park. Of the total, were designated "wild", "scenic", and "recreational".
A wide variety of recreational activities occur along the Sandy. Hiking, fishing, backpacking, and camping are popular along the upper river. Hikes include the trail to Ramona Falls, a well-known waterfall. Other uses of the upper river and its surrounds include kayaking and cross-country skiing. Fishing, picnicking, non-motorized boating and floating are among popular activities on the lower river.