Gosh, what questions meaningfull question, hehe..
Well..Littering can have many effects on the environment coz i think. It is extremely unsightly and uncollected litter can attract more. Litter can end up in rivers and canals, polluting the water supply, Animals may get trapped or poisoned with litter in their habitats. Diseases are rife in places where with high amounts of litter. Somethimes, It is also a road hazard and can occasionally contribute to accidents..
As for how to stop people from lettering. In my opinion,To strengthen the people's consciousness for enviroment protecting is priority. And doing punishemnt. For example in many western countries littering is punishable by 100 - 750 Euros.
So Terrible, ya? Hehe..