A state judge agreed on Monday to temporarily block the first passenger-vehicle ferry service between the Hawaiian Islands from using Maui's Kahului Harbor, giving environmental groups a victory.

Protesters sought the temporary restraining order to halt the Hawaii Superferry from using the harbor until an environmental assessment is conducted. The request does not affect ports on Oahu or Kauai.

The environmentalists argued in a lawsuit that the ferry's plan to ply 400 miles of Hawaii waters each day endangers whales, threatens to spread invasive species and will worsen traffic and pollution.

Superferry officials have said the ship's water jet propulsion system means there are no exposed propellers to strike aquatic animals.

The order remains in effect until Sept. 6. On Wednesday, the judge will hear arguments on a request for a preliminary injunction.

Hawaii Superferry Inc. said the company was hopeful it would prevail at the hearing Wednesday and resume operations to Maui on Thursday.

While the order did not include Kauai, the company also met with opposition on the rural island, where hundreds were gathered late Monday for the vessel's arrival.

About 65 protesters entered the water - some using surfboards, kayaks and canoes while others just swam - to block the harbor. Their effort was supported by about 200 protesters on shore.

Coast Guard vessels, including an 85-foot cutter, worked to clear the way for the ship.

The Superferry started trips on Sunday, two days ahead of schedule, after the state Supreme Court ruled last week that the state should have required an environmental assessment before the ferry launched. State transportation officials, noting that the court didn't explicitly say the ship couldn't run, allowed the service to start.

An attorney representing three environmental groups, Isaac Hall, said state law clearly says that a project cannot be launched and state land cannot be used until an environmental assessment is being prepared.

Before Sunday, the only way to travel among the islands where an estimated 1.3 million people live and tens of thousands of tourists arrive each day was by the local airlines.

The $95 million ship is built to carry more than 800 passengers and 200 cars. After Sept. 5, the fares will go up significantly: Round trips from Honolulu to Maui or Kauai, with taxes and a fuel surcharge, will cost more than $240 for one passenger and a car.