Transportation- In the olden days most people got around by carriage or boat. These days we use cars, buses, taxis, trucks etc. Because of this, we have caused major air pollution in some cities and countries. Before human settlement the air was clean and clear.

Litter- Before humans settled, there was not the risk of plastic rubbish, cigarette butts, milk cartons, paper cups, rubber, metal etc. Now most food or drink comes in an non environmentally friendly wrapper, and because irrisponsible humans come along and throw their rubbish everywhere it causes major pollution in our waterways. 

Land clearing- As humans came along we have cleared millions of kilometres of land to make schools, buildings, businesses, restaurants, cafes etc. By doing this we are clearing loads of native scrubbs and vegetation.

Dumping- Many humans dump household waste such as rubbish, oils, fertillizers, lawn clippings etc. Eventually these things will end up in our waterways. 

Greed- The health of the earth has decreased due to humans not caring about the environment and caring more about fancy cars, money etc. Also many humans are so lazy that they cannot be bothered to discard their rubbish etc properly, instead they through it in the river etc etc...