In the early morning hours of June 24, 1989, the Uruguayan-flagged oil tanker M/V Presidente Rivera ran aground on Claymont Shoal, a rock ledge in the Delaware River, spilling an estimated 200 to 307,000 gallons of No. 6 fuel oil as the vessel was preparing to dock at the Sun Oil Company refinery in Marcus Hook, Pennsylvania. River and tidal currents spread the oil, impacting approximately 29 miles of riverine and estuarine shoreline in Pennsylvania, Delaware, and New Jersey. The most heavily oiled areas were located along a three mile span of shoreline immediately south of the Port of Wilmington in Delaware. The highly viscous oil formed a thick coating along the shoreline about five to 20 feet thick. Because of the tar-like consistency of the oil, vacuum and supersucker trucks, conventional skimming weirs, and sorbent pads and booms were ineffective. The large amount of debris in the river mixed with the oil, further complicating cleanup operations. Nontraditional methods, including the use of hopper barges, clamshell bucket dredges, and a fishing vessel equipped with a stern trawl net, were used to remove oil from the water. The oil spill impacted bird and blue crab populations, with documented crab mortality and a three week closure of the blue crab fishery, as well as diminished the recreational use of the lower Delaware River during the summer of 1989.