From New York, to Virginia and now into North Carolina, 333 dolphins have washed ashore so far this summer.
Testing on 32 of 33 of those animals has revealed an outbreak of a disease called "morbillivirus".
It's similar to the measles that occurs in humans but scientists say this outbreak poses no health threat to people.
The affected dolphins often have skin and brain lesions, along with other infections because the disease suppresses their immune systems.
"This event is frightfully similar to an event that occurred in 1987," said Charlie Potter a Smithsonian scientist.
That's when more than 750 washed up along the east coast also because of the morbillivirus.
Scientists expect the outbreak to spread south and possibly last until next spring.