Nice, while swimming the length of the Thames, David Walliams contracted the diarrheal infection Giardiasis, from the exposure to sewage contaminated water. And tore a disc in his back. Giardiasis or ‘beaver fever’ is an infection of the small intestine by a single-celled organism called Giardia lamblia, that breeds by laying eggs in your intestines and multiplying daily, causing abdominal cramps, watery diarrhea, foul flatus and fever for 3-4 days, before proceeding into a more sub-acute phase. So bad that for people with compromised immune systems, such as elderly or AIDS patients, it can be deadly. Read The Sun