Habitats, clean water and green cities

A habitat is the place where an organism lives. Every habitat gives food, water and shelter. If one of these is taken away or used up, we say the habitat is destroyed. Some causes are natural: forest fires, floods, volcanoes and disease. Even these can sometimes help: a volcano can leave fertile soil, and some seeds only open after a fire. Other causes come from people: clearing land for farms and buildings, building roads, pollution and rubbish. An invasive species is another cause. It arrives from elsewhere and harms the natives. In the Nile and canals, the water hyacinth, a plant from South America, can cover the surface and block light and air for the water below. The lionfish lives naturally in the Red Sea, but in the Mediterranean Sea it is an invader. Climate change is now also altering habitats, because the temperature and rainfall they need are changing.