Months after the US government declared the waters in the Gulf of Mexico safe, thick layers of oil have been found along Louisiana coastal marshes, prompting local officials to accuse relevant authorities of ‘cover-up.’

Louisiana officials say parts of the state’s coastline are still being fouled more than eight months after British Petroleum’s (BP) Deepwater Horizon rig caused the biggest oil disaster in the United States.

“This is the biggest cover-up in the history of America,” AP quoted Plaquemines Parish President Billy Nungesser as saying.

On Friday, Robert Barham, secretary of Louisiana Department of Wildlife and Fisheries, joined Nungesser on a tour of the area.

“It has been eight months since the Deepwater Horizon oil rig explosion, and five months since the well was capped. While workers along the coast dedicated themselves to cleaning up our shores there is still so much to be done,” Barham said in a statement.

The heavily saturated area that reporters saw was 30 feet (9 meters) to 100 feet (30 meters) wide in sections.

“There’s been no mechanism to clean that up thus far,” the parish president said.

“Every day, this shoreline is moving inland,” lessening flood protection for residents, Nungesser added.

This is while US President Barack Obama and one his daughters went for a swim in the Gulf of Mexico last summer in an attempt to portray the water as safe and boost tourism industry reeling in the affected areas after millions of barrels of oil leaked into the gulf.

Nungesser has been a frequent and outspoken critic of the cleanup effort ever since the oil explosion began infiltrating the environmentally delicate Louisiana coast line in April 20.

The wildlife and fisheries department, meanwhile, said oiled boom remains in “numerous locations, forgotten or lost by contractors charged with their maintenance and removal.”

The officials said biologists have found several oiled birds in the past few days, including at least two dead brown pelicans.

The explosion that destroyed the BP-leased Deepwater Horizon rig killed 11 workers and, according to the government estimates, led to more than 200 million gallons (757 million liters) of oil spewing from a hole a mile beneath the Gulf of Mexico.