Generic Trash in a Generic Stream

While driving on a back road towards Ithica, I noticed something interesting about the stream that had been running along side the road. It was littered with trash. There were multiple plastic pottles, an egg carton, a few newspapers/magazines, and some other unidentifiable plastics. At the end of this stream was Cayuga Lake, which is a problem. But an even bigger problem is that this could be a stream on any road that leads to any lake. Why do people feel the need to throw their trash out into the environment? How can we change people's attitudes to make them understand that this behavior needs to change? And how can we encourage people who live near the trash to help clean it up, even though it is not their fault?