Since the first dolphin carcasses washed up in New Jersey and Virginia in June, more of the marine mammals have been found stranded and dying in Maryland and New York.
"When we were doing examinations, we would find they were very skinny animals," biologist Kim Durham, whose rescue team has recovered 27 dead dolphins, told CBS News. "They were compromised animals. Some of them had skin lesions -- they were just very sick individuals."
Marine biologists say they believe the animals may be carrying a bacterial or viral infection with symptoms that resemble measles.
"There's a lot of skin contact among them," Durham said. "They're constantly rubbing each other, so yeah, the possibility that they're spreading it among themselves is very large."
A virus was found to be responsible for a similar die-off in the late 1980s.
Pollution may be weakening dolphins' immune system, said Smithsonian marine mammal biologist Charles Parker, who investigated the 1980s incidents.
"As the animals migrate south, passing back through Virginia and are going down to the Carolinas, if this event follows what we saw in 1987, we can expect the epicenter of the epidemic to move south with the dolphins," Potter said. "It will run its course, but there's no way to know when the end will come."