It comes as a surprise to many people, but the sea off the south east of England is a perfectly decent temperature for swimming for at least two months of the year - from mid July to mid September. This section describes all the swimmable beaches within a day's rail trip from London, as well as the walks on this website that lead to them.
Some general tips are given below. For individual beaches, see the area menu at the top of this page.
Alternatively you can use the interactive map to find a beach in your area - just click on any beach symbol on the map to get more information on that location.
When is it warm enough?
Sea warms up more slowly than air or land, and the best time for swimming lags a bit behind the best temperatures of summer. On a hot sunny day in June (yes, they do happen sometimes), the sea can look awfully enticing, but if you plunge in, you will find the water is icy cold - around 12-14 degrees. By early July the temperature is usually bearable, however, and by late August the sea can feel quite balmy, with temperatures as high as 19 degrees.
In September temperatures start to slide, but it is more lower air temperatures that put people off swimming at this time than colder seas. By the end of the month, water temperatures are a little nippy at 16 degrees, but that is only the same as they are in mid July. Temperatures dip sharply from then on, however, and by mid October they are back to where they were in mid June. The sea is actually at its coldest (7-8 degrees) at the end of February.
It is important to note that the sea temperature is not influenced by the weather day to day. It is as warm on a grey overcast day as on the following day when the sun is hot, and should be as warm in the early morning as in the late afternoon. However on shallow beaches the sand or shingle heats the incoming tide on a hot day, and strong sunshine also warms the surface water, as well as warming your body as you swim. This effect can be reversed if there is a strong offshore wind - that is, the wind blows the warmer surface water out to sea and it is replaced with colder water from the deeps. An influx of fresh water - from heavy rain or a river outlet - can raise sea temperatures locally.
A harmless bit of sediment
The sea off the south coast is never clear - it always looks a bit murky. But this is sediment, not pollution. Look around you at the soft chalk cliffs or crumbling muddy shoreline and you will understand why the English Channel is not as clear as the sea off Cornwall. But actually bathing water standards are pretty stringent these days, and you will find many south coast beaches proudly showing off their European Blue Flag, proving they have met a rigorous EU water hygiene standard. Particularly in towns, the local council would probably be warning you if the water was not fit to swim in. (This is not the same as saying that the sea is as antiseptic as a municipal swimming pool - but tens of thousands of people swim in it each summer without incident.)
A (very rare) exception to all this is after really heavy rain: sometimes this overwhelms sewage treatment plants, meaning raw sewage ends up in the sea. An example came in 2008, when heavy rains caused the Marine Conservation Society to downgrade their assessments of some English beaches, and advise swimmers not to use them after heavy rain: but even then nearly all South Coast beaches got at least a basic pass for cleanliness. You can see the MCS's latest recommendations on http://www.goodbeachguide.co.uk/.
- If sediment in the water bothers you particularly, try and swim at high tide, when fresh clean water has flowed in from the open sea. By contrast, just after low tide, the water can be positively brown (due to stirred up sediments) on beaches with a long, flat bottom. In general, the water gets clearer the further out you swim.
- Though rich in marine life (see the enormous cuttlefish bones that sometimes wash up on beaches) the sea off the south coast seems relatively free of any creatures that bother humans. You get the occasional story in the newspapers about exotic foreign jellyfish being seen off the coast of Devon, but the author has been swimming in the Channel for years and has never heard of anyone being bitten, stung or stabbed by anything. If you are worried about this, however, wearing swimming shoes (see below) offers some reassurance.
- South coast beaches are - with a few exceptions - shingle (ie pebble) beaches, so walking down to the water's edge - or more to the point, getting out of the sea - can be a painful business if you are barefoot. A pair of rubber-soled swimming shoes is the easy solution, available for around £5-6 from beach shops, sports shops, or anywhere that sells diving equipment.
- Don't go out of your depth unless you are a confident swimmer, and before you do go too far into deeper water, check the way the currents are flowing (which you can do by staying still, and seeing which way you move in relation to objects on the shore, such as the place you left your clothes). Fortunately, currents tend to be flowing parallel to the shore on the south coast - they go up the Channel (ie eastwards) when the tide is rising, and down the Channel (westwards) when it is ebbing (though locally currents sometimes seem to be the reverse of this). Note that currents can be stronger further away from the shore, however, and avoid the mouths of rivers (eg at Cuckmere Haven)
- It is useful to know the state of the tide before you swim, especially on beaches with long flat sections where the sea can come in or go out rapidly. Information on high and low tides up to six days ahead can be found on the BBC website. Confusingly, the times given here are in GMT: add an hour to get the time in British Summer Time.