A high tide and big swell combined to make the right conditions for a surfer on the commute home from work.
Instructor Reuben Mellor-Clark, 21, had finished surf lessons at Perranporth in Cornwall when he spotted a wave on the river.
So he jumped in and rode it for a short section of his journey home on Thursday.
The so-called Perranporth Bore is created when waves are squeezed into the river channel leading to the beach.
And it was the combination of a high spring tide and a big swell rolling in from storms in the Atlantic that created the wave, said Mr Mellor-Clark of the Perranporth Surf School.
“With high spring tides the waves come in a lot further and when big waves come in they are pushed all the way up into the river,” he said.
Swells around the Cornish coastline have been created from the remnants of former Hurricane Sam which has been bringing big waves across western Europe., according to surf website Magic Seaweed.
Surf lessons were cancelled on Friday morning at Perranporth as the high tide and swell created a lot of white water and conditions that were “not ideal” for learners.
The RNLI warned everyone to beware of “strong rip currents” created by the conditions.
“As well as stronger currents, spring tides increase the risk of being cut off as the tide comes in faster than usual,” said a spokesperson.
“We urge anyone thinking of going in the water over the next few days to consider their ability, and to check the surf and tide conditions in detail before planning any coastal activity.”