The whale, said to be more than 10 meters in length and sighted Saturday morning, was found some 15 nautical miles southeast of the isle of Fårö, which lies on Gotland's northern tip. The Coast Guard's vessel Triton followed the animal during the day at a distance so as not to frighten it.
Whale sightings in the Baltic are very rare, reports Swedish Radio's local channel on Gotland, and the crew has contacted whale experts in Gothenburg.
"It's impressive, to see such large animals. It comes up every three, four minute for air and then you hear a snorting sound," boat captain Claes Jakobsson told the station.