After nearly two weeks, Oskar Kihlborg and Sören Kjellkvist paddled into downtown Stockholm Sunday evening after starting their trip some 230 kilometers away on the island of Gotland.
The duo made the journey on stand-up paddle boards, which looks like a surfboard powered by an long oar.
The trip was co-organised by Stockholm University's Baltic Sea Center to help raise awareness about micro-plastics polluting the water. During the journey, the adventurers trawled fine-mesh nets to collect items for research analysis.
Sören Kjellkvist tells Radio Sweden that the algae caught in nets would be given to the University for testing.
"We want to see where the micro-plastics are; what happens to them when they get out into the ocean," he says. "The micro-plastics are so small you can't see them with your eye."
Kjellkvist adds that the trip was a first and left the pair in need of some recovery.
"I got home Sunday evening and slept like a log the whole night," he says. "We really exhausted ourselves."