Safe swimming: what's lurking in the water?

More and more of us, it seems, are rediscovering the pleasure of open water swimming. But bathing in the sea, lakes, streams, ponds or rivers can be risky to your health unless you take sensible precautions. 

Here’s how to make sure you don’t catch or encounter anything nasty when taking the plunge.

Before you take the plunge

Five tips from the River and Lake Swimming Association:

  • Only swim in rivers and lakes if you’re a good swimmer.
  • Don’t jump or dive in.
  • If in doubt, don't go in water that's too deep to stand up in.
  • Don’t swim after drinking alcohol or eating a heavy meal.
  • Never swim alone, in case you need help.

Jellyfish stings

Jellyfish are responsible for the most stings in the sea around the UK and the problem is set to worsen as jellyfish numbers rise. UK jellyfish stings aren’t dangerous, but they can lead to an intense, stinging pain, sometimes with itching and a rash.

The Marine Conservation Society has produced a useful guide to different types of UK jellyfish. Their stings vary, but some species, like lion’s mane, are particularly painful.

What to do: Avoid swimming in jellyfish-infested areas, and never touch a jellyfish. According to the National Poison Information Service, neither urinating on a jellyfish sting nor applying vinegar will help. 

The best treatment is to remove any remaining tentacles using tweezers or a clean stick. Applying an ice pack to the affected area will help reduce pain and inflammation.

Find out what to do when you get stung by a jellyfish.

You can also occasionally get stung in UK coastal waters by weever fish, stingrays and sea urchins.

Read more about marine stings.

Shark attacks

Believe it or not there are at least 21 types of shark in British waters including the Catshark, Blue Shark and toothless, plankton-eating Basking Shark. But don't worry, it really IS safe to go in the water. According to the Shark Trust, shark attacks are incredibly rare with many more people killed or injured each year by bee stings, snakes, crocodiles or tigers.

The Trust adds that you're highly unlikely to encounter a shark during a trip to our seaside. In any case, most British sharks are completely harmless with only two reports of unprovoked attacks by sharks in European waters since 1847.

Tummy upsets from sewage in the sea

Swimming in sewage-contaminated sea water can cause a range of illnesses from gastrointestinal (digestive tract) and respiratory infections to ear, nose and throat complaints.

Many beaches in Britain have excellent water quality, others less so. The amount of sewage contamination varies from beach to beach.

What to do: To minimise the risks of swimming in polluted water, pick a Blue Flag beach or one recommended by the Marine Conservation Society (MCS). The Good Beach Guide is published by the MCS and indicates which UK beaches have excellent water quality.

Find out how to find clean sea water to swim in.

Getting too cold

Outdoor swimming in cold water saps your body heat so your arms and legs get weaker and you could get into trouble if you’re unable to get out.

What to do: If you’re not used to swimming in cold water, the Outdoor Swimming Society recommends that you wear a wetsuit for anything more than a quick dip. It also advises that you:

  • Don’t jump into cold water – instead, wade in slowly.
  • Swim close to the shore.
  • Take warm clothes to put on afterwards as, even in summer, you’ll feel colder when you get out.
  • Take extra care in reservoirs, which are deeper and colder than lakes and rivers.

Shivering and teeth chattering are the first symptoms of hypothermia. If that happens, get out of the water and warm up. Read more about treatment for hypothermia.

Blue-green algae

Blue-green algae can appear on lakes and ponds over summer, forming a powdery green scum. Swimming in it can trigger skin rashes, stomach upsets and sore eyes.

What to do: Avoid swimming in lakes that have areas of blue-green algae.

Finding clean freshwater spots

Our rivers and streams and lakes are less polluted with chemicals and germs from sewage spills and animal waste than they’ve ever been. But not all of them are clean enough to swim in and could trigger stomach upsets and infections.

What to do: Generally, if the water looks clean and clear, it’s a good indication that it’s safe to swim in. If it’s scummy or cloudy, it’s best to avoid it.

The Environment Agency monitors the water quality of our rivers, streams and lakes regularly at over 7,000 locations. The Agency’s website can give a water quality rating for the stretch near you when you enter your postcode into their site.

Weil’s disease

Weil’s disease (also known as leptospirosis) is a bacterial infection spread by animal urine, especially that of rats. It tends to be found in urban rivers and canals, but you can also catch Weil’s disease in still water such as lakes, either by swallowing contaminated water or, more likely, by getting it into your bloodstream through a cut or graze.

What to do: Cover any cuts with a waterproof plaster before swimming and avoid swallowing the water. Never swim in an urban canal. If you develop symptoms of Weil’s disease within a few weeks of being in water, see your doctor. The condition can be treated with antibiotics.

Read more about Weil’s disease.

Tummy bugs from sewage in streams, rivers and lakes

You can end up with diarrhoea and vomiting after swimming in sewage-contaminated streams, rivers and lakes. The main culprits are bugs such as E. coli and Cryptosporidium, which can be spread by swallowing water from lakes, streams and rivers containing sewage or any kind of animal or bird droppings.

What to do: To reduce your risk of tummy bugs, don’t drink from streams even if they look clear. Cows or sheep may have urinated in them. Wash your hands after paddling in a river or stream and avoid swallowing water while swimming.

Read more about tummy bugs and how to treat them.

Swimmer’s itch

"Swimmer’s itch" (cercarial dermatitis) is an itchy rash caused by certain parasites that live in freshwater snails. The snails live on the reeds around marshy lakes and stagnant ponds. On warm, sunny days the parasites can be released into the water and burrow into the skin of swimmers.

What to do: Although uncomfortable, the itching generally lasts no more than a couple of days. You can’t spread the rash to other people, and it doesn’t need treatment.

To reduce your risk of swimmer’s itch, avoid swimming or wading in marshy areas where snails are commonly found and rinse off as soon as you leave the water.

Page last reviewed: 05/06/2014

Next review due: 05/06/2017


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