Like you, this was a question I had going into college...what major could I pick that would help me one day conserve the environment and educate others regarding this issue. I ended up majoring in biology with a focus in ecology and conservation. Then I went back to school to get a certificate in wetland science & management which helps me in my work as an ecologist where I find wetland and stream boundaries and help to preserve these spaces.
Looking back on my undergrad, I wish I had majored in environmental science - this gives you an opportunity to cover a wide range of issues (ecology, conservation, global warming - it varies depending on the school). You could also look into fisheries, if that interests you.
Another piece of advice I have is - yes, we both love the environment, but how do you translate that to a job where you can make a living? In this field there are different types of employers (private, public/government, non-profits - ordered from higher to lower paying *generally). Definitely consider what kind of work you're preparing yourself for. The natural resource management field is rich with job opportunities (forestry, wetlands, water quality, etc), because a LOT of people only care about the environment in regards how it relates to money and functions/values that relate to humans.
I hope there was some insight in there!