Researchers say a record number of dolphins are washing ashore this summer.

The Riverhead Foundation for Marine Research says 15 dolphins have washed ashore this July compared to three last July.

Marine biologists don't know why dolphins have been washing up on beaches.

The Riverhead Foundation is leading the probe. Experts say it's possible that warmer water temperatures could make it harder for dolphins to fight off disease, but say that's just one of many causes they're investigating.

A dolphin that recently washed ashore in New Jersey tested positive for a respiratory disease. Researchers are now testing to see if the dolphins that washed ashore on Long Island have the same illness.

The Riverhead Foundation urges people not to approach dolphins that have washed ashore. Until they figure out what the mystery illness is, experts say there's no way of knowing if it could be harmful to humans.