The Thames Barrier has been raised every day for the last fortnight to allow as much water as possible to drain out of the upper Thames without flooding central London.
All well and good but that means that when the high fluvial levels (posh term for flow) combine with the tidal ebb the current is really rather strong - four times normal according to the Evening Standard. In fact dangerously strong.
The Port of London Authority (PLA) has therefore introduced a new web-based ebb tide safety flag indicator system and it's currently saying "Extreme Warning".
You can find the flag on the PLA's web site for recreational river users, boating on the Thames. There's even a widget you could stick on your own site.
To help explain why this really is serious look at the image above, which is a rowing eight stuck against a barge. As can be read here:
Their rowing eight was driven under boat moorings and broken in half by the strength of the tide.
Canoers, kayakers and sailors should also take note.
As an extra warning, have a read of this article about what is contaminating the water - yuck!
Extreme warning indeed.