Three people have been arrested after about 200 revellers attended an illegal rave at a protected nature reserve.
The rave was held at Kirkstall Valley Nature Reserve in Leeds on Monday night.
West Yorkshire Police said people had waded across a section of river to gain access to the reserve, sparking concerns for their safety.
A local community group said they also disturbed nesting birds and could have trodden on some of the young birds.
Supt Chris Bowen said the force wanted to encourage people to play by the rules, but would use enforcement powers where necessary.
"We would urge people to consider their own safety and the safety of others, particularly during the warmer weather and the ongoing period of lockdown," he said.
Sound equipment was also seized by officers.
The reserve is a protected area and is used as a nesting ground for several species of birds.
Posting on Facebook, the Kirkstall Valley community group, which campaigns against fly-tipping and anti-social behaviour, said it was appalled.
The group said the revellers would have scared off many waterfowl species, leading to their young being abandoned.