Take I-5 north through the border at Peace Arch State Park in Blaine. Drive about 18 miles north on Highway 99 in B.C. Take Highway 17 west to 56th Street. Turn left on 56th Street and follow it to the Point Roberts border crossing.
Once you enter Point Roberts it is only 2.5 miles from the border to the park. Go straight on Tyee Drive, and follow it past the marina. Keep following the same road along the water until you reach Lighthouse Marine Park on your left-hand side.
Map to the Park