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 reduce your risk of swimmer's itch: 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.
The plane will also be used to transport members of the Royal Family and will still be used for its regular job of refueling other RAF jets while they are flying.