Several small boats were destroyed when they crashed to the ground after being thrown into the air by the rotating column.
A number of people were at or near the harbour at the time, enjoying a calm day in the almost 30 degree heat. There were no reports of any injuries.
The first signs that something was amiss came when a life vest, sand and some rubbish suddenly came to life.
“There was a perfectly clear sky, 29 degree heat and no wind. Then, with no warning at all, this started up. An incredible force of nature,” one witness, who wished to remain anonymous, told news agency TT.
The man was sitting in a parked car some 50 metres away when he saw the tornado circling above a collection of small boats in dry dock.
“It was almost like watching a UFO as these little boats were sucked up one after another and just swirled around in the air,” said the witness, who estimated that the tornado kept the vessels in its clutches for around half a minute.
“People were screaming at each other to grab hold of something,” he said.
But the tornado disappeared almost as quickly as it had arrived.
“The boats came tumbling down one by one. One of them was up quite high, maybe 30 to 40 metres, and came tumbling straight down,” said the witness.
The tornado then moved out over the lake and dissipated.
“Then we were able to go out, It felt like it was raining a little but it was just water from the lake that the tornado had brought with it into the air,” he said.
Tornadoes are a relatively rare occurrence in Sweden, according to Jan-Olof Ringman from meteorological agency SMHI.
“We usually get reports of maybe five a year,” he told TT.
“Swedish tornadoes generally progress just a few kilometres before dying out. In the countryside they are hardly even noticeable. It’s not like the American Midwest, the homeland of tornadoes,” Ringman added.