High Quality Content by WIKIPEDIA articles! The High Line Canal is a man-made waterway, used for irrigation and recreation, that serves the Denver-Aurora Metropolitan Area. The High Line Canal (HLC) begins at a diversion dam on the South Platte River, some 1.8 miles (2.9 km) above the mouth of Waterton Canyon. From its headgate, the HLC runs 66 miles (106 km) to Green Valley Ranch, passing through Douglas, Arapahoe, and Denver Counties.