The Guide Meridian travels through the western outskirts of Lynden and passes through an industrial area and near the Northwest Washington Fair and Events Center. The highway leaves Lynden and narrows to two lanes before reaching an intersection with SR 546. After traversing another stretch of farmland, SR 539 reaches the Lynden–Aldergrove Border Crossing on the Canadian border, where it terminates. The highway widens to accommodate two separate lanes for trucks and NEXUS pass-holders and is split into two roads with a duty-free store in the middle. The border crossing is open from 8 a.m. to midnight and is the fourth-busiest border crossing in the state, with 509,467 vehicles entering the United States in 2017. Beyond the border, the road becomes British Columbia Highway 13, which continues north to Aldergrove and an interchange with the Trans-Canada Highway east of Langley.