Here are some facts about effects of the worst ever U.S. oil spill, triggered by the April 20 explosion of the Deepwater Horizon rig:

THE SCALE OF THE CATASTROPHE

"This is probably the biggest environmental disaster we have ever faced in this country," top White House energy adviser Carol Browner said on Sunday.

"There could be oil coming up 'til August." Browner told CBS's "Face The Nation," "We are prepared for the worst."

Louisiana, the nearest state to BP's gushing undersea well that is 42 miles out in the Gulf of Mexico, has been the most impacted by the spill so far.

Louisiana Governor Bobby Jindal said this week that more than 100 miles of Louisiana's 400-mile coast had so far been impacted by the spilled oil.

State officials have reported sheets of oil soiling wetlands and seeping into marine and bird nurseries, leaving a stain of sticky crude on cane that binds the marshes together.

Billy Nungesser, president of Plaquemines Parish, saw dying cane and "no life" in parts of Pass-a-Loutre wildlife refuge.

"Oil debris", in the form of tar balls and surface "sheen", has also been reported coming ashore since the April 20 accident in outlying parts of coastal Mississippi and Alabama.