Premise: A 15ft (4.5 meter) northern bottle-nosed whale has been spotted swimming in the river Thames in Central London, UK. The "Thames whale" managed to swim up past the Thames barrier and under many bridges, reaching as far as Chelsea before it turned around just before Albert Bridge. TV news helicopters scrambled to provide live TV footage of the whale, and many spectators lined the banks of the river. The whale is said to be looking healthy, although some fear that the whale may beach itself as it tried to do before rescuers forced it back into the middle of the river. Normally found in the North Atlantic, there have been sightings of a second whale near Southend.
Hypothesis: Some whales are  bottle-nosed.