The clean-up has begun after an illegal weekend rave in Pembrokeshire.
Seventeen arrests were made, ten cars impounded and sound equipment worth £100,000 seized after 2,500 people descended on the village of Dale.
Residents reported that the revellers had left their rubbish in piles of bags, but these had been attacked by seagulls.
Ten people are in custody after the rave.
The cost of the clean-up has been estimated as £3,500 by the Pembrokeshire council.
Sharon Bryan, who farms the land used for the rave with her husband Michael, described the events of the weekend as "horrendous".
"There's a lot of rubbish and human waste that's also been left," said the tenant farmer.
"It frightened me," she said. "We've got two young children.
"My husband Michael does blame himself for not doing what he could but I feel that the position that we were all in at the time, when you've got 300 cars that come in in one swoop, we just couldn't do any more."
"This is our land," she added. "We've got a lot of stock up here at the moment which we've been worried about.
"Our neighbours have been rallying around and helping us, moving tractors and trailers, trying to contain the revellers."
There were no facilities at the rave site, including an absence of toilets. Party-goers had said they intended to clean the site before leaving.
However, Supt Reg Bevan, of Dyfed-Powys Police, said there was a "significant amount" of debris left as the event wound down.
He said: "The council were there last night commencing the clear-up, and there were a few individuals who were attempting to clear up the site who had been party to the celebrations there.
"But the vast majority of people had left the place in a considerable mess."
Neighbouring farmer Owen Morgan told the BBC: "There are gulls everywhere".
A spokesman for Pembrokeshire Council said a refuse truck was sent to the site at Dale at 1700 BST on Monday to start collecting some of the rubbish bags left behind by ravers.
Council workers were going back on Tuesday to see what was left, said the spokesman.
One reveller told the BBC that he regretted that those who attended the event had not been given sufficient time to clean up behind them.
"If they'd given us time, we'd have cleaned up the place," he said. "We've been told we have to leave so we've got to rush out.
"Except for the rubbish, which I do not like, there's really not a lot wrong with the place."
Another criticised what he said were "ridiculous" health and safety laws.
"The number of festivals this year that have been cancelled," he said. "The health and safety laws and regulations are getting absolutely ridiculous.
"They are shooting themselves in the foot and then they wonder how things like this happen."
Police and council officials said they planned to gather information on the organisers with the intention of prosecuting them.
Supt Bevan told the BBC: "It was a wholly inappropriate location when you've got single road access to a site that's on the edge of a cliff, smack bang in the middle of the national park.
"We were unable to prevent them arriving at the site. But what were were able to do, through using our helicopter, was to identify who we believe were the main instigators and organisers on the site and as they've left we've arrested them."
Supt Bevan said 10 of the 17 people arrested were still in custody.
Officers were looking at offences under the Licensing Act as well as other offences of damage that had been committed on the site, he added.