A mega-pod of dolphins spanning across 7 miles of ocean was spotted off the coast of San Diego.

An estimated 100,000 adult and juvenile common dolphins were filmed swimming and soaring together by a group of lucky tourists on a boat last Thursday, according to Captain Joe Dutra of Hornblower Cruises, who also spotted the dolphins while sailing his daily tour.

Dutra said that the dolphin pod was more than 7 miles wide and 5 miles long. He told local media that the boat tour followed the super-pod of dolphins for more than an hour, reports The Telegraph.

"When you see something that is honestly truly beyond belief," Dutra told NBC San Diego. "They were coming from all directions, you could see them from as far as the eye can see," he said.

"I've seen a lot of stuff out here... but this is the biggest I've ever seen, ever."

Dolphins are social mammals that live in groups called pods. They travel in groups of 200 or less. Yet, researchers say that the sighting of a super-pod of dolphins is not unheard of. Marine mammal expert Sarah Wilkin told NBC that the availability of an abundant food source like squid, herring and sardines could bring the small dolphin groups together.

But how did so many dolphins gather into a mass crowd in the same place? The dolphins may have learned about a "prey patch" of fish and squid through echolocation, Monica DeAngelis, of the National Marine Fisheries Service, told KFMB San Diego. Echolocation is the biological sonar used by dolphins to detect objects in their environment by sensing echoes from the objects.

Click here to look at the mega-pod of dolphins filmed by tourists on a boat off California coast.