at Sauvie Island
At the far end (bottom) of the bridge, you'll see the Cracker Barrel Store ahead on the left. Buy a one-day or full-year parking pass there. Parking passes are required in all Wildlife Area parking lots, including those near the beaches. The police do issue tickets.
Drive UNDER the bridge onto Gillihan Road. Follow Gillihan Road until it ends.
Turn right onto Reeder Road. Follow Reeder Road until it becomes gravel. (You'll have already passed the main part of Walton Beach, with parking areas on the left and concrete steps on the right.)
About 1/4 mile after Reeder Road becomes gravel, you'll see signs on the right: "Collins Beach, Clothing-Optional Area, Nudity on Beach Only." Five such signs identify the five trails onto Collins Clothing-Optional Beach. They're numbered as #2 through #6.
Park on the left, display your parking pass, and follow a trail to the beach.
Do NOT undress in your car or in the parking lots: undress only after you reach the beach. Nudity is NOT appropriate in the parking lots or on the road.
Do NOT exit Collins Beach at the north or south boundaries while nude. Do NOT exit to the road or parking lots while nude. When you see signs saying "Leaving Clothing-Optional Area", cover up or stop.