The grey seal decided the best way to navigate the River Orwell in Suffolk was to bask in the sun while solo sculler Terry Davey did the hard work.
Mr Davey, 71, from Felixstowe, told the Ipswich Star the animal jumped on board several times before eventually settling down.
"He was so relaxed he nearly fell asleep at one point," Mr Davey said.
A founder member of Deben Rowing Club in Woodbridge, Mr Davey was sculling from Woodbridge to Ipswich on Sunday when he was joined by the seal about 18 miles (29km) into the 25-mile (40km) journey.
"I took a break for some water and a biscuit, and this seal arrived and started resting his head on my oars," he told the BBC.
"It was really cute, like a dog might rest its head on your lap.
"I said, 'come on, boy', a few times - and he put his flippers on the boat and clambered aboard."
Mr Davey said he had twice had grey squirrels hitch a lift across the river on his boat, but never a grey seal.
"He jumped on and off several times. He was sitting there with his head over the side under the water, looking for fish. He'd jump off and then come back."
The seal was with him for about 30 minutes, he said.
Mr Davey eventually completed his journey in five hours - without his new companion on board.
"I'd have done it a lot faster without that bloomin' seal," he said.
A seal took a break from swimming in a river to hitch a ride on the end of a rower's boat.