Glastonbury Festival organisers have been ordered to pay £31,000 after 20,000 gallons of untreated sewage leaked into a stream, killing protected fish.
A steel tank which was used to store waste from festival-goers leaked into Whitelake River, causing the deaths of 42 fish, including brown trout.
Despite the fine, handed down by Bristol magistrate's court, the district judge said the festival had "low culpability" for the incident.
The incident happened during the 2014 festival season and the Environment Agency claimed that the music event was so popular that it was struggling to deal with so much waste.
More than 4km of the river was affected.
The popular Somerset festival attracts about 175,000 people each year.
Glastonbury Festivals Ltd admitted breaching environmental regulations and was fined £12,000 and ordered to pay £19,000 towards prosecution costs.
District judge Simon Cooper said that he was satisfied there was proper planning for the festival and he was "impressed" by how responsive Glastonbury Festivals Ltd have been, the Guardian reported.
He added: "I am bemused at the vigour and energy that has been put into this detailed analysis of what happened, much after the event.
"I am sure lessons will be learned. I shall say no more about it, save to say that cooperation is clearly essential and I hope that this hearing has done nothing to affect that.”
Speaking after the case, Ian Withers of the Environment Agency said: ”The festival is held in a beautiful part of the Somerset countryside and we want to see it remain that way.
“This was a serious pollution incident that had a significant impact on water quality and the fish population of the Whitelake River over some distance.”
The festival's founder, Michael Eavis, said that he thought the court case was a "waste of time" as organisers did their "very best" when they discovered the leak.
Eavis wanted to assure festival-goers that no such leaks will happen again in the future.