Thames Whale
Here is a picture of the whale as it passed underneath Vauxhall Bridge. A pretty amazing and singular sight, people were literally walking along the side of the thames to keep up with it as it was chaperoned by a police boat and a lifeboat. At one point someone got into the water at the side to herd it away from the bank as the Thames is currently at low tide and there is probably a danger of it getting beached (for want of better word for the Thames' shorelines). The sight of a spout of water coming from the water was a little surreal. I watched from outside Tate Britain and then watched it swim underneath the bridge and off towards Battersea.
The BBC has live coverage here, and the Guardian's take is here (although they seem to be dwelling on the fact that it may be in some sort of distress). The Londonist is also following the story now ('The Voyage Home'...). Apparently it's a Northern Bottle-Nosed whale which usually only swims in these waters to the North of the U.K, so quite why it fancies a sojourn in the Thames is anyone's guess...
UPDATE: Sadly it has died on the barge being used to transport it back to deeper waters.