An unusually high number of dead dolphins - including stillborn and infant calves - have washed up along the Gulf of Mexico shores in the two years since the Deepwater Horizon oil rig exploded into flames, unleashing tens of thousands of barrels of oil into the ocean.

In a normal year before the spill, about 74 strandings would be reported in the area. That number has increased eightfold in the past two years. Since February 2010, more than 600 have been found on the shores between the Louisiana-Texas border and the western coast of Florida.

A dead zone the size of the state of New Jersey is growing in the Gulf of Mexico, fueled by nutrient runoff from the swollen Mississippi River.

Scientists say it may become the largest dead zone ever.