Drilling in Arctic waters is bitterly opposed by environmental groups and some Alaska Natives. Their lawsuits and permit appeals have prevented Shell Oil Co. from drilling in the Chukchi Sea, where the subsidiary of Royal Dutch Shell PLC spent $2.1 billion on leases in 2008. Shell also holds older leases in the Beaufort Sea and hopes to drill exploratory wells this summer in both locations. Environmentalists say the anchorage problem is yet another reason to question Shell's plans.