Swimming in tidal rivers like at Burnham can be really dangerous – here’s why:
The gravitational effect of the moon means that twice each day a massive tidal wave moves along the English coast from north to south. As this tidal wave approaches the level of water rises –the ‘Flood Tide’– and as it passes the river falls – the ‘Ebb Tide’. When the moon is closest the tidal wave it pulls along after it is largest – so called ‘Spring Tides’ and when its farther away the tidal wave is smaller – ‘Neap Tides’. Right through the year we have this fortnightly cycle – a week of Spring Tides followed by a week of Neap Tides. On Spring Tides the levels rise higher and fall further – there’s a lot more water moving around, so tidal streams are much stronger than on Neap Tides.
In Burnham, like in most tidal rivers, the Ebb Tide tends to run more strongly than the Flood Tide. In particular, very soon after high water the tide turns and starts running strongly towards the sea. The current sweeps round the bend opposite Creeksea and then runs down strongly close along the north shore of the river through Burnham town – right past the pontoons and jetties on which it is so tempting to sunbathe and take a dip.
You may not notice that the tide has turned. You may not see that all the moored boats are straining back on their mooring chains. Very close in to the seawall it may not be very obvious, but out near the ends of the pontoons the tide may quickly start to run at up to five knots – that’s a very swift walking pace and much faster than you can swim!
It may be a split-second decision to throw off your shirt and jump in – but if you do so on a Spring Ebb you’ll just as quickly be in deep trouble: If you try and swim against the current you’ll quickly run out of strength. Maybe wiser to go with the flow and try to edge over back towards shore, where the current will be less strong, but if you fetch up against the up –tide side of a pontoon or jetty you’ll be at risk of being dragged under it if there’s no way of quickly climbing out.
Only a fool chances his or her life in a situation he or she does not understand. Perhaps our advice not to swim is unwelcome – but to do so without knowing what the tide is doing is madness. At the very least you can find out on this website where there are free Tide Tables for the whole year showing the times of the two high waters and two low waters each day (clock times) and the heights of high and low water. As a guide any high water with a height of 4.5m or more is a Spring Tide, which are the ones that run most strongly and really need to be avoided, especially on the ebb (ie. after high water). But even the Neap Tides can have strong currents – so unless you really are confident of your strength as a swimmer, best only go into the water very close to the shore, within your depth, where the tide runs slowly – don’t jump into deep water from the end of one of the pontoons!