(MONEY Magazine) – Environmental charities face mountainous obstacles these days. Donations-up just 2% last year-have leveled off since a surge after the 20th anniversary of Earth Day in 1990. Since these charities rely on relatively small donations for most of their income, they must spend a lot on fund raising. And now environmentalists are under attack from the "wise use" movement, which argues that conservation efforts such as blocking logging to save the spotted owl cost jobs. Despite this tough atmosphere, the National Wildlife Federation (NWF), Money's most efficient conservation charity, is raking in money-and members. Last year, NWF's income rose 6% to $92 million, with about a third of the money coming from its 1.8 million dues-paying members. (For $16 a year, members get merchandise discounts, a newsletter, and a subscription to one of NWF's magazines.) The sale of catalogue items such as T-shirts and stuffed animals brought in another $30 million. The money goes mostly to support the NWF's educational programs such as publishing National Wildlife magazine and Ranger Rick for kids, taking city dwellers camping in its NatureLink program and advising schools on curriculums. (The charity's focus on education differentiates it from the No. 2 group, the World Wildlife Fund, which also promotes animal preservation.) The NWF keeps expenses down by carefully researching the cost-effectiveness of potential programs before launching them. On the activism front, these right-to-wildlifers aren't exactly flamethrowers. Unlike most other environmental groups, National Wildlife supported NAFTA.