Staff at the Dorset centre spotted the otter walking through the external areas of the centre until it sat in the coffee shop entrance for a few moments before moving on.
Staff member Chris Woods, who filmed the otter on his mobile phone camera and video, said: "We are about a kilometre from the River Stour and there are no other real streams nearby, so it travelled quite a way – maybe it was because we had tuna mayo jacket potatoes on the menu that day."
Otters, which are viewed as a barometer of river health, did not completely disappeared from Dorset rivers as they did from other UK areas, and after years of decline, their numbers are now significantly increasing.
An Environment Agency survey of 3,327 rivers has found otters have increased 10-fold between 1980 and 2010.
Better water quality and a hunting ban are behind the increase.