World Environment Day was started at the 1972 Stockholm Conference on the Human Environment, and has been celebrated internationally since 1987. It was set up to raise awareness and encourage environmental action, and it prompts activities by all sorts of people all over the world.

Last year people in 110 countries took part in activities to consider how we use and treat water. The theme was 'Water, 2 billion people are dying for it'. This year we are thinking about water again, but this time about the seas and oceans and the life that depends on them, as we ask 'Wanted: seas and oceans, dead or alive?'.

UNEP / Ingrid Kavanagh

Over the years young people have created art, essays and poetry on the theme of the day, and exhibitions of their work, street marches and parades have done a lot to raise awareness. Trees have been planted, art and fashion crafted from waste, wells dug, botanical gardens created and rivers, parks and beaches cleaned up - among a host of practical environmental activities. Then there are public debates and discussions on environmental issues between people from the media, art, academic, business and sporting worlds, and many others.

This year World Environment Day is being celebrated on 4 June in Barcelona, as part of a three-month long cultural festival in the city - which should make the environmental campaigns, street rallies, parades and musical concerts even bigger and louder than usual.