A lot of factories produce waste and is drained into rivers. So the water in the rivers becomes poisoned.
The hole in the ozone layer is very dangerous to humans: ultraviolet radiation passes through them and reaches the Ground. Such radiation may cause dangerous diseases.
The population of many countries is suffering from lack of water.
Nuclear weapons can produce terrible destruction on our planet. Nuclear power plants are not so “clean” as some believe: they become the source of the contamination.
The environment is everything you see around you. Today people understand the need to keep it clean, if humanity wants to survive.