If you are not corrupt, the money is pretty good—you're looking at around $70k per year on average. If you ARE corrupt, you can green light all kinds of projects and make a bundle, although it will likely come in cash in suitcases. What do you think BP would pay for an enviro to tell people that the Gulf spill is now cleaned and A-OK?
When just starting out, you'll be taking home around $35k annually, but it can go up quickly from there, and you could easily hit the $50k threshold within just a couple of years, then be making $75k or more in less than a decade.
Government jobs tend to pay the best; if employed by a private company, you're generally going to be making $10-15k less. Part of the reason for this difference in salary is that our government has a ton of extra cash on hand, due to them not having a huge debt or anything. Cough, cough.