HOUSTON (Reuters) – A giant oil slick in the Gulf of Mexico has not spurred shipping restrictions in US Gulf channels like the vital Mississippi River, the head of the US Coast Guard said.

The oil slick from last week's deadly offshore oil rig explosion is creeping eastward across the Gulf, threatening the coasts of Louisiana, Mississippi, Alabama and Florida.

The spill's current trajectory is between the Southwest Pass, the main deepwater shipping lane into the Mississippi River, and navigable channels for vessels to Gulf Coast ports, Coast Guard Commandant Admiral Thad Allen said on a conference call with reporters.

The spill has not affected shipping lanes – called fairways – that giant oil tankers and barges follow to gain access to the Mississippi River or other important ports like Gulfport, Biloxi and Pascagoula in Mississippi, or Mobile, Alabama, Allen said. "Right now there is no significant impact of the oil on those fairways, but we are watching that," Allen said.

"The potential exists that that could happen as the spill moves around and potentially moves toward Mississippi and Alabama," Allen said. "There are no impacts at that time and we have a protocol to handle it should it happen."

Those could include stopping shipping traffic through spill-affected waters, or allowing vessels to travel through the spill and then decontaminating their hulls before they continued, Allen said. The rig Deepwater Horizon, owned by Transocean Ltd., sank on April 22, two days after it exploded and caught fire while finishing a well for BP Plc 42 miles off the Louisiana coast. Eleven workers are missing and presumed dead after the rig exploded.