Swimming in the sea

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, and some even swim as mid June. The walks on this website visit a number of pleasant spots for taking a dip. Below are details of some of them - and some insider tips to help you make the best of them

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, the sea can look awfully enticing, but if you plunge in, you will find the water is icy cold - around 12-13 degrees early in the month, though this climbs to 15 or 16 degrees by its end. In July the sea temperature then climbs to around 18 degrees, and stays there throughout August. 

By early September the sea temperature is declining slightly, but more importantly the air temperature is lower and many people no longer think of going to the beach. The air temperature also has an effect on the temperature of the top layer of the sea. When days are longer and the sun is hotter, the upper 30 centimetres or so of the sea become a degree or two warmer. In September, as nights get longer and the air temperature cooler, this effect lessens. So a 17 degree sea can seem colder in September than than it does on a hot day in July. It is usually falling air temperature, rather than falling sea temperature, that brings an end to sea swimming for the year.

For the same reason, the sea tends to feel warmer later in the day than it does in the early morning (when the sun or air temperature has had less time to warm it up). If you go for two or three swims in a day, you will also find that your body becomes more accustomed to the sea temperature and it feels warmer as the day goes on. Strong sunshine can also warm your body as you swim, and on shallow beaches the sand or shingle may heat the incoming tide a bit on a hot day.

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 (at least until Brexit) nearly all south coast beaches met rigorous EU water hygiene standards. 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: but even then nearly all South Coast beaches got at least a basic pass for cleanliness. You can check out their water quality rating of any British beach here

  • 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.
  • Though rich in marine life (see the enormous cuttlefish that sometimes wash up on beaches, having come from the deep ocean to breed in our waters and then die) 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.

Handy tips

  • 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 - broadly, they go up the Channel (ie eastwards) when the tide is rising, and down the Channel (westwards) when it is ebbing. Note that currents can be stronger further away from the shore, however, and avoid the mouths of rivers.
  • 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 weather website.

Beach Guide

Anticlockwise: From Worthing to Brighton to Dover to the Thames

Fairlight Glen

Further west

The beaches of the Isle of Wight and Hampshire are also accessible from London on a day trip, though as fares tend to be in the higher £20s even with a Network Card, these are probably only options as a summer treat.

Essex coast

Last updated: September 2010

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