Sewage in the sea
Swimming in sewage-contaminated sea water can cause diarrhoea and vomiting, as well as infections of the ear, nose and throat.
Many beaches in Britain have excellent water quality, others less so.
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.
Read more on how to find clean sea water to swim in.
Sewage in streams, rivers and lakes
You can also end up with diarrhoea and vomiting after swimming in sewage-contaminated streams, rivers and lakes.
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.
- Generally, if the water looks clean and clear, it's a good indication that it's safe to swim in.
Read more about tummy bugs and how to treat them.
Getting too cold
Outdoor swimming in cold water saps your body heat, so your arms and legs get weaker. If this happens, you could get into trouble if you're unable to get out of the water.
If you're not used to swimming in cold water:
- wear a wetsuit for anything more than a quick dip
- don't jump into cold water – wade in slowly instead
- swim close to the shore
- take warm clothes to put on afterwards – 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 can appear on lakes and ponds over summer, forming a powdery green scum.
Avoid swimming in lakes that have areas of blue-green algae. Swimming in it can trigger skin rashes, stomach upsets and sore eyes.
"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.
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.
- Rinse yourself off as soon as you can after getting out of the water.
UK jellyfish stings aren't dangerous, but they can lead to an intense, stinging pain, sometimes with itching and a rash.
Avoid swimming in waters crowded with jellyfish, and never touch a jellyfish.
If you get stung:
- remove any tentacles using tweezers or a clean stick
- apply an ice pack to the affected area to help reduce pain and inflammation
Peeing on the sting or applying vinegar won't help soothe it. Find out what to do when you get stung by a jellyfish.