BOULDER CITY - National Park Service officials are blaming low water levels and a decline in business for the upcoming closure of the Echo Bay Marina fuel dock and boat slip facility on the northern part of Lake Mead.Bill Dickinson, superintendent of the Lake Mead National Recreation Area, said no bidders sought the 10-year contract for water-based services at the facility in the Overton arm of the lake."It is unfortunate that we have to ask people to leave the Echo Bay Marina after they have spent years vacationing here," Dickinson said.Forever Resorts, a concessioner that operates several other marinas on …