Scientists have found a decline in oxygen levels in the Gulf of Mexico following the BP oil spill but have found no "dead zones" as a result, the National Oceanographic and Atmospheric Administration reported Tuesday.

Levels of dissolved oxygen in deep water have dropped about 20 percent below their long-term average, according to data collected from up to 60 miles from the well at the center of the massive oil spill. But much of that dip appears to be the result of microbes using oxygen to dissolve oil underwater, and the decline is not enough to be fatal to marine life, said Steve Murawski, the head of a NOAA-led group examining the spill's impact.

"Even the lowest observations in all of these was substantially above the threshold," Murawski said.