Over time, your efforts, and those of the friends and family you brought to it can make a significant difference. But keep in mind a prime directive - don't sacrifice other places for yours. Educate yourself and educate others. Learn all you can about the different linkages of issues and science in your watershed. As you learn, share it.
Personal communication is the most effective means of learning and changing.
As you know more, pass it along to others in email, letters to the editor, friends and people you meet, anywhere and everywhere, and learn from them at the same time. Best is to become expert enough on some aspect of your watershed and participate in any stakeholder or other decision-making processes. State, federal and local agency public processes are biased towards those who know the most about an issue and have the most information. Become one of those people yourselves. Get involved in the watershed group where you live.