Ruby Arm is a scenic, narrow inlet forming the southernmost section of Ross Lake within North Cascades National Park in Washington State. It is a freshwater lake arm, not a tidal coastal feature. Access for paddlers is unique due to the lack of direct road access to Ross Lake. The primary method is a paid shuttle service operated by Ross Lake Resort, which transports boats and paddlers from the Diablo Lake boat launch around Ross Dam to a drop-off point on Ross Lake, opposite the resort. An alternative, more strenuous option is to carry gear down the East Bank Trail to reach the water's edge of Ruby Arm, though this involves a significant portage. The lake is known for strong afternoon winds that can create challenging conditions, making many paddlers prefer to stick to the lower end of the lake unless entering from the far north. The length of the lake and these wind patterns mean a paddle into Ruby Arm from the main drop-off point is a commitment of several miles. The arm itself is noted for its forested, mountainous scenery and offers access to specific features like cliffs suitable for swimming and jumping near Hidden Cove. Several backcountry, boat-in campsites are located along the shores of Ross Lake, including some up Ruby Arm, such as Green Point Campground. A backcountry permit from the National Park Service is required for any overnight stay. The water is clear and cold, with the surrounding peaks providing a dramatic backdrop. The overall experience is one of remote, flat-water paddling in a rugged wilderness setting, with logistics that require advance planning for shuttle services and permits.