The National Park Service wants to ban personal watercraft such as Jet Skis from most of the waterways it manages, saying they are dirty, noisy and dangerous.

They would be banned from all national parks, including nine where they are now allowed, under rules the agency has proposed. The parks that would be affected include Biscayne, Big Bend, Isle Royale, Olympic and Voyageurs.Jet Skis would still be allowed at 13 other units administered by the Park Service, 11 national recreation areas - including Utah's Lake Powell - and two national seashores, Gulf Island and Padre Island, at the discretion of the local superintendent. The prohibition would be delayed for two years at a dozen other units, mostly national seashores and lakeshores, to allow for further study.

"Our mandate is to protect these places and to provide for the visitors' use of them, to ensure that they will continue to be here as they are now for future generations," Park Service spokeswoman Elaine Sevy said Tuesday.

Park superintendents were recently told not to allow any additional use of Jet Skis while the new rules are in the works.

Park Service officials plan to publish them this summer and then take public comment for 90 days, after which time the rules may be revised. They are not expected to take effect for up to a year.

"We've still got quite a ways to go," said Dennis Burnett, the Park Service's regulations manager.

Personal watercraft makers have opposed the ban as unfair and unnecessary, arguing that new models are quieter and cleaner. Their users are becoming more courteous and safer, they say.

Americans now own 1.2 million personal watercraft and sales are running at 200,000 a year. They account for 11 percent of all watercraft registered in the country but 35 percent of the accidents involving vessels.

In proposing its ban, the Park Service said personal watercraft are "often operated in an aggressive manner" and are the subject of frequent complaints about noise and unsafe operation. In addition, leaking oil and gas can foul the water.