**Please note: This event has been cancelled due to weather conditions **
King Cnut couldn't hold back the tide, but the Thames Barrier can. During a test closure on 29 September, hundreds of craft will take to the water for the annual mass-paddlesports event, Regatta London.
How to join in
Regatta London will see 800 boats and 1,600 paddlers enjoying a Thames free of tides and shipping. It's a unique chance to kayak, canoe, paddleboard or row through central London without the hazard of other river traffic.
You can sign up to either of two courses. The Big Ben Challenge is a 12 mile loop from Putney to Westminster and back. The London Crossing goes from Hammersmith or Putney to Greenwich.
The best way to sign up is through one of the three headline charities, so you can have fun while raising money for a good cause. These are waterways charity Thames21, London Youth Rowing and mental wellbeing champions Mates in Mind.
How to watch
If you're not an able seaperson, then you can still enjoy the day by visiting the events areas on Putney Embankment and at Greenwich. These will have a family-friendly street party feel, with live music and food & drink stalls. Most importantly, you can watch at a finish line and cheer on the paddlers.
Regatta London is on 29 September along the Thames from Hammersmith to Greenwich from 7.30am. Entries for kayak/canoes close at 11.59pm on Monday 26th August.