I love the National Wildlife Federation. I have not done research into nature groups, and maybe (I honestly don't know) there are other organizations that are better, more effective, etc., but I always get a wealth of knowledge and information from their monthly magazine.
For example, many people would not know this, from the Aug/Sep issue of National Wildlife (also for the photo credit). I sure didn't:
Southern Mississippi's Pascagoula River starts with the wedding of the Chickasawhay and Leaf Rivers near the former timber town of Merrill and cuts lazy S-curves through verdant forests, swamps and floodplains to the Gulf of Mexico. It is 80 miles long and drains a watershed the size of Vermont.
In a 1994 study of rivers in the northern third of the world, the journal Science identified this undammed, unlevied, undredged vestige as the largest free-flowing river system in the lower 48 states. Naturalist and Pulitzer Prize-winning author Edward O. Wilson, who grew up in nearby Mobile, Alabama, says places like the Pascagoula "are the closest thing the south-eastern United States has to wilderness."
That is one interesting factoid, that every other river of any significance in North America, has been either dammed or levied or dredged. Kinda sad, that civilization has progressed (?) so far.
The concern of the NWF is that:
...the Pascagoula is threatened by a proposed Strategic Petroleum Reserve depot, a proposed port expansion, periodic dam proposals and the prospect that large timber tracts will be subdivided once the real-estate market rebounds.
This is why contributing to such groups, who can serve as a focused advocate for conservation, is such an important thing, even as many of us have tightened our belts thru these tough economic times.