Bosses of the festival admitted at a court hearing in Yeovil, England on Thursday (14Jan16) that the 2014 event had breached British environmental regulations.
Prosecutors acting for the U.K. Environment Agency told the court they launched an investigation after being alerted to increased levels of ammonia in the Whitelake River, which runs past the rock event's Worthy Farm site.
During the hearing, bosses of the festival company pleaded guilty to violating environmental permits, and Eavis subsequently issued an apology, revealing sewage had leaked from a tank being used to store human waste.
"Of course, I'm exceedingly sorry for what's happened. We had a problem obviously - there were 200,000 people and we were storing slurry," he told the BBC.
"It was a tank for holding farm slurry, but on this occasion we were using it for the festival sewage and it was starting to leak. It was a brand new build, it cost me £100,000, so that's my defence."
Prosecutors for the Environment Agency asked court officials to impose a fine of between $82,500 (£55,000) and $450,000 (£300,000) on festival bosses, alleging that a number of endangered fish had died as a result of the leak.
Lawyers acting for the festival disputed this, and the case has been adjourned until 31 March (16) when a date will be set for a new hearing to establish the facts of the case and decide upon the penalty imposed.