The Glastonbury Festival is under way after suffering serious disruption when storms tore across its site at Pilton, Somerset, on Friday morning.
Heavy rain flooded parts of the site, with dozens of tents lost under water, while lightning strikes affected the stages and knocked out power lines.
Bands such as The White Stripes, Doves and The Killers are due to play at the event, with 112,500 people expected.
No serious injuries were reported, but conditions are expected to stay muddy.
Ambulance staff reported nine emergency cases, but none of the people involved turned out to be seriously injured.
Organisers said under 100 tents had been washed away, and facilities had been set up to hand out clothing and new tents for those affected.
Streams running through the site burst their banks at the height of the storm, with some gates to the site closed because of waterlogging. Portable toilets sank in the mud, as did one of the bars.
One festival-goer was even seen swimming to his tent to retrieve his belongings - something medical staff are advising against.
Festival-goers have also been advised to wash their hands after using the toilets, and not to eat food which has been in the water, because of the risk of bacteria from the sunken toilets.
Broadcasters were also affected - the set constructed for BBC Three's coverage from Glastonbury was flooded while Radio 1's Jo Whiley had to abandon her live broadcast after a river close to the corporation's compound burst its banks.
Local fire crews assisted in pumping the water off the site.
Festival founder Michael Eavis told the BBC News website: "People survived, and coped. We need to cheer up a bit and enjoy ourselves. If you get a challenge like this it wakes everyone up and it improves the spirit."
He urged people not to be put off coming to the festival.
"Come on down, you will have the time of your life, but bring your wellies," he told Radio 1.
"Don't be put off by a bit of rain. We've seen it all before and we will cope."
Heavy rain continued until 1100 with intermittent showers and thunderstorms, mixed with sunshine, after.
Police said over 100,000 of the expected 112,500 crowd were on site by Friday evening, and they had dealt with 88 drug offences and 21 other reported crimes.
Four police horses had to be moved out of the festival after their stables flooded.
Most of the crowd have already been on the site for one or two nights and had been enjoying a party atmosphere before the rain fell.
Elvis Costello, Royksopp and Bloc Party are among the other stars appearing, while Coldplay headline on Saturday. Basement Jaxx will close the festival on Sunday.
Live 8 organiser Bob Geldof will address crowds at from the Pyramid Stage on Saturday.
One of the dance tents turns into a silent disco at 0100 on Saturday in an attempt to reduce noise for neighbours.
Rain hit the site from early in the morning
Other attractions on the 100 acres of farmland include a cinema field, early morning bingo and children's areas complete with fairground rides and puppet shows.
The Green Fields offer information, workshops and therapies from outside the mainstream while scores of stalls sell everything from global cuisine to clothes, toys and jewellery.
Friday alone should see more than 100 musical acts performing across nine main stages.