Three years ago, British couple Michael and Margaret Snell travelled to the Vancouver area for a fishing trip and thought they hit the jackpot, reeling in a sturgeon that was 1.5 metres.

But that trophy pales in comparison to the massive fish the retired couple caught in the Fraser River during a return trip this week, hauling a white sturgeon out of the water that measured nearly four metres and weighed half a tonne — believed to be one of the largest fish every caught for sport in North America.

The couple, from Salisbury, England, set out onto the Fraser River from Chilliwack, east of Vancouver, on Monday.

Story continues below advertisement

Michael Snell, 65, said he saw his rod tip, but he struggled with his catch for nearly 45 minutes before he actually saw the fish surface.

It was 3.8 metres long.

"We just saw a tail fin come up, then a bit later we saw a middle fin, and eventually, as it got tired, we saw the head come out as well," he said in an interview on Friday.

"We realized the sheer length of this fish — next to the boat, it's nearly as big as the boat."

The couple's guide, Dean Werk, said he knew right away Snell had caught something huge. Snell's wife, Margaret, had to hold on to his harness to keep him from being pulled into the river.

"(The fish) peeled off 200 yards of line on its first run without even a blink," said Werk. "We had to chase it down, we had to stay close to it, and Michael was having to work the fish back up, trying to keep it near the surface."

The couple and their guide eventually brought the white sturgeon onto the shore.

Story continues below advertisement

Once Werk was in the water with the fish, he noticed the animal wasn't tagged, indicating it may never have been caught before.

Werk estimated the sturgeon was at least 100 years old, weighing roughly 500 kilograms. Based on a database kept by the Fraser River Sturgeon Conservation Society, Werk said it could be the largest fish ever caught in the continent.

They released the sturgeon back into the river, but not before snapping some photos with it.

Snell, who has been fishing since he was a little boy, said it took several days for the size of his catch to sink in.

"I could only get my arms halfway around the (sturgeon's) head," he said. "It's so big, like a wine barrel or a 50-gallon oil drum."

"Here I am, holding a dinosaur, virtually. You watch it breathe, watch it blow. ... You just marvel at this fish."