Kevin Williams of Anchorage was paddle boarding last Thursday on the glassy waters of Passage Canal near Whittier when a large, silvery fin appeared just a few feet from his board.

For most of the afternoon, as he paddled, he and his son, Brian, had been watching the humpback whale from a healthy distance.

“But then it went under for quite a long time. And then all of a sudden it surfaces right in front of me. And it’s coming towards me sort of like a submarine,” Williams said in an interview Wednesday.

His son was further away and snapped a photo. The whale had moved directly below Williams’ board.

Williams said he dropped to his knees for stability. He was terrified. The whale was clearly immense, he said.

“It was a scary encounter. It was not a comfortable experience,” he said. “I dream about seeing whales up close. But not this close. Not while on a paddleboard.”

Then there was a big splash, and then the whale was gone as quickly as it had come, Williams said. The fin had missed his board by inches, he said.

His other son, Erik Williams, later shared a photo of the encounter on social media, showing the whale’s giant fin rising directly in front of Kevin Williams’ board.

“If you blow up my picture you can see it’s almost like a scream. I was groaning and moaning pretty loud. I’m glad it wasn’t on video,” Williams said.

While the encounter ended well for Williams, it was objectively a dangerous one, said Suzie Teerlink, a Juneau-based marine mammal specialist with the National Oceanic and Atmospheric Administration.

Grown humpback whales can weigh 40 tons and are often more than 40 feet long. They spend summers in Alaska, and migrate to more tropical waters, typically Hawaii, in the colder months. Humpbacks were listed as endangered for several decades but most of their populations have recovered, including the ones most commonly found in Alaska waters. Prince William Sound is a common feeding area for humpbacks.

Humpbacks are not known to show any aggression towards humans and typically try to avoid them, Teerlink said. But close encounters sometimes occur, particularly while the whales are preoccupied with other activities such as eating — which they do about 20 hours a day.

Teerlink said there have been cases of humpback whales that have breached on or near boats and injured people. But it doesn’t happen often.

“There’s so much mass there that even, you know, a subtle swipe of a pectoral fin could really injure or kill a human,” Teerlink said.

Under federal regulations, it’s unlawful for boaters or paddlers to intentionally get within 100 yards of a humpback whale off the shores of Alaska. In certain situations, like the one Williams found himself in, that is not always possible, Teerlink said.

“We can’t always predict where (the whales) are going to come up. And sometimes we might predict wrong, or they change direction. And we’ll have a close encounter,” she said.

Her advice for anyone in a similar situation: “Give ‘acoustic cues’ to the whale to let them know that you’re there; so, banging on the top of a paddleboard, something like that would help generate noise into the water to help clue the whale into where you are.”

Her more general advice is to always give whales a wide berth when you see them while out paddling, given how very large they are.

Said Williams, “I’m glad they got a few pictures. I would not be able to tell this whale’s tale if they hadn’t had photos. I don’t think anyone would believe me.”