As if the cold weather didn't already chill San Francisco's tourists, one of the most popular boat tours has been suspended for safety precautions.

The Ride the Ducks boat tour company indefinitely suspended tours nationwide after one of is amphibious duck boats sank after catching fire and being rammed by a barge on the Delaware River in Philadelphia on Wednesday. Two people are missing.

The company operates seven boats in San Francisco and the boats can easily transition between the water and the road. Dozens of tours are offered each day, said General Manager Cory Roebuck.

But because of the accident those tours are canceled and hundreds of dollars of refunds have been issued, Roebuck said. All seven of the fleet's boats are being inspected again as officials in Pennsylvania are still investigating the cause of the accident.

Many tourists who had booked seats on the 80-minute tour through the streets and shore of San Francisco seemed to take the cancellation in stride. Tours are $32 for a regular-priced adult ticket.

Ride the Ducks offered to give those with reservations a complimentary city bus tour.

It doesn't go in the water, but it's better than nothing.

"He's probably more disappointed than I am," said Barbara Wilkerson, referring to her 6-year-old son, Malcolm, who was bracing against the cold next to her on the front seat of a motorized cable car.

Wilkerson, who just arrived from Colorado, booked their trip on the Duck before they left home. She said she hoped the rest of their trip would continue without incident.

Claudia Reif of Modesto said she came to the city with a friend specifically to ride the amphibious boat.

Reif said she had ridden the boats in a number of cities and enjoyed the view from the water.

The company called her to let her know the tour would be canceled, but she said she decided to come in to the city for the bus tour anyway.

"I'll still get to see everything on the street," she said.

Bay Quackers, a competitor of Ride the Ducks, continued to operate its three amphibious ducks just down the street. But the company has no plans to capitalize on Ride the Ducks' temporary closure, said David Perry, a company spokesman.

"We certainly would not want that sort of image to get out there," he said.

Eli Brown, an employee at the Bay Quackers booth at Fisherman's Wharf, said there hadn't been a spike in ridership because of the competitor's closure.

In fact, he said, business had been a little slow, which he attributed to the weather and not tourists' safety concerns.

"Normally on days when it is overcast like this, things are usually quiet," he said.

Roebuck, the general manager, said it was prudent for the company to temporarily suspend the tours until the accident's cause is determined.

"We miss our Ducks and our passengers. It'll be back to normal soon," he said with a sigh as a packed Bay Quackers boat drove by.