Flanaburg said he was fishing when the shark latched onto his kayak.
"It was intense. It was just like the Discovery Channel where you see the eyes roll to the back of the head and the pink gums and his teeth bared," he said.
"It almost instantly, the shark came and it hit the bottom of the boat, lifted the boat up, and grabbed ahold of it and just started shaking the whole boat, and I'm just hanging on to this thing," he added.
Flanaburg said that the force of the shark's bite launched all his supplies into the air, including a bottle of home brew.
“I was pretty much helpless, just hanging on for dear life,” he told CBS San Francisco, and estimated that the shark was about 12 feet long.
Flanaburg walked away from the incident unharmed, but beach officials will post signs warning the public.