Viral video captured a rattlesnake under a Tampa Bay bridge. How rare is that?

Capt. Brett Norris averages about 300 boat trips a year under the Tierra Verde Bridge — but only one has ever included a rattlesnake.

The fishing charter captain was driving his boat the morning of Oct. 27 when, as he neared the underside of the bridge, a flash of snakeskin caught his eye.

He moved his boat closer, and sure enough: An eastern diamondback rattlesnake was curled on a railing about three feet off the water. Its rattle was raised in the air, warning the crew not to come any closer. Norris and his two clients from Baltimore had trouble believing what they were seeing.

“I turned around and I was like, ‘Oh man! That’s for real! That’s a real-deal rattlesnake,’” Norris said in an interview. “It was kind of startling. You don’t really see that kind of animal just out in the open, right in the middle of where everybody comes through every single day.”

Norris filmed his encounter with the 4-foot snake and shared it to his Instagram page, where it was viewed more than 18,000 times. It was then picked up by larger fishing accounts, amassing more than 300,000 views as of Tuesday morning. “People from out of town like to see manatees and dolphins. But to see a rattlesnake? Maybe I need to start doing rattlesnake charters here pretty soon,” Norris joked.

Two Florida snake experts with decades of shared experience both agree: It was an uncommon sighting. But with diamondbacks native to Florida and residing in all 67 counties, it’s also not terribly surprising, they said in interviews. The animals were here long before us, after all.

“It’s definitely not common, but it’s likely a snake that dispersed from a nearby landmass and is taking a break,” said Melissa Miller, an assistant research scientist at the University of Florida’s Institute of Food and Agricultural Sciences. “It’s a cool sighting, nonetheless. When you go fishing, you’re not expecting to see a diamondback out in the wild.”

Eastern diamondback rattlesnakes prefer terrestrial environments (Weedon Island in Tampa Bay, for instance, is known among the angling community for its rattlesnake sightings). But they’re also incredible swimmers, according to Miller. Anglers have reported seeing the snakes 10 miles offshore in the Gulf of Mexico. And when they get tired, they coil up, inflate themselves with air and bob along in the water like a cork.

“They’re extremely good swimmers, and saltwater isn’t a problem for them,” said Kevin Enge, a research herpetologist with the Florida Fish and Wildlife Conservation Commission. He’s studied snakes for more than three decades, and believes this particular animal was swimming offshore of Tierra Verde during high tide when water levels were elevated. It probably got tired and found the nearby platform under the bridge. When the water dropped with an outgoing tide, the animal probably became stuck, not willing to make the 3-foot free fall into the water below.

So it waited there. And along came Norris in his boat, whose first thought was “I don’t want to get too close to the sucker” followed by, “That’s cool as hell!”

Miller agrees the animal swam there, maybe from nearby Fort De Soto Park. The bridge where Norris filmed the video is nestled between the park to the west and Tarpon Key to the east. It was probably just taking a breather in between, Miller said.

The Eastern diamondback is one of six venomous snake species native to Florida. Their population here and among most of its southeastern range is starting to decline, according to the Florida Fish and Wildlife Conservation Commission. A misunderstanding of the species, often driven by fear, have historically led to mass-killing events like “rattlesnake roundups.”

That’s one reason why Norris’ video of his rattlesnake encounter in a busy public space is so unique.

“It’s a very cool snake that gets overexploited,” Miller said.