Park at the Gentle Falls Overlook parking lot. Observe the sign cautioning that the steep downhill path is not maintained by the park. Go down that path. My daughter insisted on it, and she led us roughly 300 feet down to this wonderful noisy whitewater scene. Take very good hiking boots and a pack for your camera, you'll need both hands to support yourself on the steep path.
Canon 28-120mm IS lens at 28mm, F/9, 1/250th sec, ISO 400
Any season is good in Blackwater Falls State Park. This viewpoint is downstream from the centerpiece falls of the park, looking upstream.