A beluga whale that was suspected of spying for Russia after being discovered in Norwegian waters five years ago has been found dead, according to the non-profit organization that had been monitoring the whale.

The body of Hvaldimir — a combination of the Norwegian word for whale and the first name of Russian President Vladimir Putin — was spotted floating in the sea by a father and son fishing in southern Norway over the weekend, Norwegian public broadcaster NRK reported.

"Hvaldimir was not just a beluga whale; he was a beacon of hope, a symbol of connection, and a reminder of the deep bond between humans and the natural world," the Marine Mind NGO said on social media.

Hvaldimir was wearing a harness with what appeared to be a mount for a small camera when he was first found in 2019 near the island of Ingoya in Norway's north, around 300 kilometres from the Russian maritime border. The harness was stamped with "Equipment St Petersburg" in English.

The whale was very interested in people and responded to hand signals, leading Norway's domestic intelligence agency to presume he had been held in captivity in Russia as part of a research program before crossing into Norwegian waters.

Moscow has never responded to the allegations about Hvaldimir.

"It's absolutely horrible," marine biologist Sebastian Strand, who worked with Marine Mind, told NRK. "He was apparently in good condition as of (Friday), so we just have to figure out what might have happened here."

No major external injuries were visible on the animal and it was not immediately clear what caused the death, he said.