The Coast Guard is creating a new anchorage zone near the entrance to the Mississippi River to help keep ship traffic moving despite the Gulf of Mexico oil spill, the official heading the effort said Friday.

An area west of the Mississippi River entrance is undergoing a final survey to make sure it is free of sensitive undersea infrastructure such as pipelines that might be damaged by ship anchors, Commander Chris Woodle said.

The intent is to provide space for ships to anchor if the existing anchorage zone east of the river mouth becomes contaminated by oil spilling from the well that exploded April 20, killing 11 men and sinking a drilling rig.

"It's just a precautionary measure," Woodle said. "We try to keep ships out of the oil. West Bay was identified early on as a possible alternative."

The National Oceanic and Atmospheric Administration, which is overseeing a final survey of the area, plans to present the Coast Guard with its findings by Tuesday to clear the way for official designation of the new anchorage zone. So far, there has been little impact on shipping and port operations, and the Coast Guard has worked to minimize harm to the environment and the U.S. economy by readying ship-cleaning stations to speed vessels along. Only one has needed cleaning.

"Keeping maritime commerce going is important to many businesses, such as farmers who need to export their crops and the millions of stores throughout the country that rely on a constant flow of imports," a news release said.

Officials at the ports on the central Gulf Coast threatened by the spill said on Friday that ship traffic has remained normal, although some ships were adjusting their routes to avoid the spill.

"The Port of New Orleans has had no ships diverted to other ports. All container ships on regular schedule have come here as planned. Cruise ships are coming here on schedule," said port spokesman Chris Bonura.

About 600 ships have entered the Mississippi headed for New Orleans and other Louisiana river ports in the five weeks since the accident, and that level of traffic is normal, Bonura said. Officials at Mobile, Ala., the second busiest port threatened by the spill, and at Gulfport and Pascagoula in Mississippi, also said ships were arriving in port at the normal rate despite the spill.

Another indicator that maritime markets are less worried is that rates for the most common oil tanker used in the Gulf have declined to $25,000 a day after spiking to $35,000 a day, a market analyst said.

"A poor supply-demand balance has outweighed both the real and psychological effect of the spill," said Mike Reardon, vice president of marketing and research for Imarex Inc. ship brokerage.