People are being urged to help prevent illegal raves from damaging the countryside in Wales.
Illegal parties frighten residents, harm wildlife and damage the environment, Dyfed-Powys Police said.
With longer daylight hours and dry weather on the way, there are concerns raves are being planned.
Police want people in Pembrokeshire, Ceredigion, Powys and Carmarthenshire to report anything suspicious in order to help them tackle the problem.
The force said a swift response was crucial to preventing illegal festivals and parties becoming established.
Last year, more than 1,000 revellers descended on the small village of Brechfa, Carmarthenshire.
Residents said human faeces and drug paraphenalia were among the mess left behind after the four-day rave.
They were critical of the police's response and the force's police and crime commissioner, Dafydd Llywelyn, said lessons "must be learned" to prevent a repeat.
Police say social media has made it easier to organise raves at short notice and for numbers to grow quickly.
Supt Robyn Mason said: "We keep an eye on social media but the organisers of these raves know that we do that.
"There's nothing better than the local communities who see and hear things happening. Hopefully then we can deal with these events before they escalate.
"Once they start they are very challenging and it's more a case of tolerating it and dealing with the aftermath.
"It's frightening for people living in small isolated communities and there's the significant impact loud music has on wildlife and that hundreds or thousands of people have on the environment.
"If those rave-goers understood that then perhaps they would consider doing something else with their leisure time."
Natural Resources Wales said the impact of illegal raves on forests, such as Halfway Forest near Llandovery, could be "devastating" and wasted limited resources.
It has installed lockable barriers at several access points to Brechfa forest and increased patrols before weekends.
Land Management team leader Dai Rees said: "Last year's illegal rave at Brechfa Forest not only caused distress to local people but also required considerable time and money to clean up afterwards.
"We strongly urge anyone who is concerned about any suspicious activity in their local forest to report it to the police."
Know the signs
- Unusual numbers of vehicles, especially camper vans, vans or trucks
- Trespassers may inspect sites in advance
- People may approach landowners under the guise of hiring sites for activities such as gymkhanas or scout camps.