Personal watercraft will be banned in national parks and recreation areas by September 2002 except in special cases where the National Park Service can prove the machines won’t harm the environment, according to a court settlement approved by a federal judge last week. U.S. District Judge Gladys Kessler dismissed a challenge from watercraft manufacturers to a settlement reached last December between the Interior Department and the environmental group Bluewater Network. Last year, the Park Service banned personal watercraft — gasoline-powered small vessels like jet skis that fit one or two riders — from two-thirds of national parks. The settlement came about after the enviro group sued to extend the ban to all parks.