On a small inflatable boat last Friday, Evan Brodsky and two co-workers with a whale-watching tour company were on the lookout for gray whales on the Pacific blue waters of Monterey Bay, along the central coast of California.

After four hours of searching, the team had spotted only one whale.

But instead of heading back to the harbor, as the team usually would, Mr. Brodsky, a boat captain and videographer with the tour company Monterey Bay Whale Watch, said he had an “itch” that there was something they could not yet see and decided to stay out on the water.

First, the team of three spotted about 15 dolphins swimming together. It followed the small pod, knowing that dolphins are highly social marine animals that usually travel in larger groups.

Some 30 minutes later, 15 dolphins had turned into hundreds. Then there were thousands.

“I kind of just take a glance and scan the horizon, and maybe about a mile and a half from us the water literally looked like it was boiling,” Mr. Brodsky, 35, said. “It was foaming. There were so many dolphins there.”

In previous outings, Mr. Brodsky had seen pods of hundreds, sometimes thousands, of dolphins, but this was the first time that he had seen a gathering of so many northern right whale dolphins, mixed in with Pacific white-sided dolphins. In the past, he had seen only a few hundred of the species in one place.

Using his drone and past experience on the water, Mr. Brodsky estimated that there were more than 2,000 dolphins in the pod his team saw that Friday.

“The whole time we were just saying, ‘Oh my gosh, oh my gosh, this is so amazing, I can’t believe this,’” he recalled. While the team is on the water almost every day, Mr. Brodsky said that the sight of the dolphins still gave him “butterflies.”

A sighting of thousands of northern right whale dolphins in a single pod is rare, though the species is known to be gregarious and willing to congregate with others, said Dorian Houser, the director of conservation biology at the National Marine Mammal Foundation.

“The groups I have typically encountered are much smaller,” Dr. Houser said, adding that he has also spotted them in the Monterey Bay.

Dr. Houser said that he suspected that there was an abundance of food for the dolphins on the day of the sighting, causing them to gather in such a large group. There is a canyon that runs through the bay, which makes the area a “fairly unique” place that is full of nutrients and attractive to wildlife, Dr. Houser said.

Among the uncommonly large grouping of the northern right whale dolphins, Mr. Brodsky said he and his co-workers had seen mothers and their calves, which he had witnessed only a handful of times before.

The whale watchers made sure not to disturb what he called a “superpod” of dolphins by keeping a safe distance and navigating parallel to them. But at times, the dolphins would swim right next to their boat.

Mr. Brodsky had seen other superpods before, including about a month ago when he captured video of about 1,500 Risso’s dolphins in the Carmel Bay, which is south of Monterey Bay. Even so, “it’s like the first time every time” he sees the large groups swimming together.

“It’s the best feeling,” Mr. Brodsky said. “It’s indescribable.”

Christina Morales contributed reporting.