On April 20, six years ago, the world watched in shock as the largest oil spill in U.S. history unfolded before our very eyes. Disaster struck as the BP Deepwater Horizon exploded and sank, resulting to 11 people missing and never found and barrels of oil spilling for 87 days before it was finally capped in June. Six years after the tragedy, a new study reveals that the negative impact of the largest accidental marine oil spill is worse than scientists originally thought.

With the report published in the journal Marine Pollution Bulletin, the new findings showed a 19-percent increase of affected shorelines from previously published estimates, as reported by the National Geographic. Scientists from the National Oceanic and Atmospheric Administration (NOAA), along with private researchers, discovered 1,313 miles (2,113 kilometers) out of 5,930 miles (9,545 kilometers) of surveyed shoreline affected by the spill.

By length of shoreline damage, this makes the BP oil spill the largest and most extensive. While some oil were recovered or burned at sea, some washed up on the shores of Mississippi, Florida, Alabama and Texas.

Louisiana shorelines are most affected by the oil spill, particularly its coastal wetlands. In particular, wetlands were mostly affected, along with beaches.

But not only are shorelines severely affected by the oil spill. Even after six years, its negative impact still shows on the ecosystems relying on the Gulf of Mexico, particularly marine and avian wildlife, and even on communities relying on the coastal areas for their residence and livelihood.

For instance, studies showed links between the BP oil spill and the deaths of dolphins in the Gulf, as per US News. Researchers said from 2010 to 2013, there was a rise of stranded stillborn and young dolphins in the shorelines of Alabama, Louisiana and Mississippi, leading them to believe that the dolphins' mothers suffered chronic illnesses after their exposure to the spill.

Since the disaster, the NOAA also reported more than 1,400 dead whales and dolphins washed up on the Gulf's shores, calling it an "unusual mortality event" that continues to happen.

The spike in the deaths of Kemp's ridley sea turtles -- the world's most endangered sea turtles -- are also being linked to the oil spill, having most likely affected their nesting areas, as reported by WUFT.org.

But not only are marine animals affected. Birds, particularly pelicans, were severely affected by the oil spill too, as they are usually on the surface of the water to feed. Not only were they terribly oiled during the disaster, but the loss of marine ecosystem also badly affected their feeding habits.

The negative impact continues up the feeding chain. Humans, particularly those relying on the Gulf for their fishing industries, are also feeling the negative impact of the spill, even six years after.

SunHerald reported a protest by members of the Mississippi Coast fishing industry, done to remember the disaster that took away their livelihood. East Biloxi, according to fishing activist Thao Vu, used to be the world's fresh seafood capitol. But the BP oil spill has taken that away and people are still reeling from the intergenerational impact that the tragedy will continue to have.

In October last year, BP confirmed a settlement of $20.8 billion, the largest pollution penalty in the nation's history. But it looks like even after six years, it may take a much longer time for the U.S. and the world to fully recover from this ecological disaster.