The high death toll, covering an area that stretches from New York to Virginia, has been labeled an "unusual mortality event," and the U.S. National Oceanic and Atmospheric Administration (NOAA) has experts scrambling to figure out what's going on.

Based on the rapid increase in dead bodies washing ashore, and the broad geographic reach, "an infectious pathogen is at the top of the list of potential causes," according to NOAA's website.

"We realize that people are very concerned and anxious to learn what we know about the dolphin deaths that have been occurring along the mid-Atlantic coast over the past few weeks," Maggie Mooney-Seus, a spokesperson for NOAA Fisheries, told National Geographic by email.

Experts have collected quite a bit of