The Nehalem River originates in the northern Coast Range of Oregon and flows approximately 118 miles through dense forests and pastoral valleys before emptying into Nehalem Bay and the Pacific Ocean. The river system drains a 855-square-mile watershed primarily within Tillamook and Clatsop Counties, with portions extending into Columbia and Washington Counties. The mainstem begins in the Tillamook State Forest and flows generally northwest, joined by major tributaries including the North Fork Nehalem, Salmonberry River, and Cook Creek.

Paddling opportunities span the full spectrum from technical whitewater to tranquil flatwater. The upper reaches from Henry Rierson Spruce Run Campground through Nehalem Falls feature Class II-IV rapids suitable only for experienced whitewater boaters, including the notorious "Salmonberry Drop" below the Salmonberry River confluence. The middle section from Roy Creek to Nehalem offers Class I-II water with minor riffles, ideal for intermediate paddlers. The lower river from Nehalem to Wheeler and throughout Nehalem Bay provides excellent flatwater paddling for beginners, though tidal influences require careful trip planning. The North Fork Nehalem presents its own character, flowing from the Coast Range through forested canyons before joining the mainstem near Nehalem. The stretch from Aldervale to Nehalem offers 5.5 miles of scenic flatwater paddling through a spruce swamp ecosystem.

Winter and spring bring peak flows from November through May, with the river being primarily rain-fed. Summer and fall offer lower, clearer water ideal for flatwater exploration, though some upper sections may require portaging during drought conditions.

Steelhead and salmon runs occur from late summer through spring, with Chinook, Coho, Chum salmon, Winter Steelhead, and Cutthroat Trout all utilizing the system. Wildlife includes Roosevelt elk on bay islands, Great Blue Heron rookeries along the river, Bald Eagles nesting near the estuary, and Pacific Harbor Seals in tidal waters. The riparian corridor features Douglas fir, Western Hemlock, Western Red Cedar, Sitka Spruce, and Red Alder, with understory species including salmonberry and sword fern.

Major access points include Henry Rierson Spruce Run Campground, Nehalem Falls Campground, Morrison Eddy, Roy Creek County Boat Ramp, Nehalem Camp, Aldervale County Boat Ramp, Nehalem City Docks, Wheeler Marina, and Nehalem Bay State Park. The communities of Nehalem and Wheeler provide services and amenities.

The Nehalem people historically inhabited the watershed for thousands of years, utilizing extensive canoe networks for transportation and subsistence. European settlement in the mid-1800s established timber, fishing, and dairy industries that continue today. The railroad corridor along the lower river facilitated early 20th-century commerce.

Cold water temperatures year-round pose hypothermia risks. Tidal currents in the bay and lower river can strengthen significantly, particularly on outgoing tides. Afternoon winds commonly create challenging conditions on open water. The Nehalem Falls rapid requires mandatory scouting or portage. All property along the river is private except designated public access points.

Multi-day trips are feasible using Morrison Eddy and Nehalem Falls campgrounds in the upper watershed, or combining river and bay paddling with camping at Nehalem Bay State Park.