This Act is P.L. 93-205 (December 28, 1973), as amended, is one of the major federal laws protecting species and the ecosystems on which they depend. While states generally have primacy in wildlife law, this is one of a handful of areas in which federal law plays the major role. ESA is administered primarily by the Fish and Wildlife Service (and by the National Marine Fisheries Service (NMFS) for certain marine species). Under authority of this Act, species of plants and animals at risk of extinction are listed as either "endangered" or "threatened" according to the degree of risk. Once a species is listed, powerful legal tools are available to aid the recovery of the species and to protect its habitat. Over 1000 species of domestic animals and plants have been listed as either endangered or threatened. The ESA has been controversial for two main reasons: First, its standards of protection are substantive, rather than procedural, occasionally preventing activities that would lead to the taking of an endangered or threatened species or jeopardizing its continued existence. Thus, the protection of endangered salmon may result in limitations on logging around spawning habitat. Even if a given activity is rarely prohibited outright, mandatory changes or modifications of practices are not infrequent. Second, because other laws often lack the strict substantive provisions that Congress included in the ESA regarding taking of species, critical habitat, and avoidance of jeopardy, the ESA often becomes a battleground by default over larger controversies concerning resource scarcities and altered ecosystems. Like the miners’ canaries, endangered species have flagged controversies over the Tellico Dam (hydropower development versus farmland protection and tribal graves, as well as the snail darter); northwest timber harvest (protection of logging jobs and communities versus commercial and sport fishing, recreation, and ecosystem protection, as well as salmon and spotted owls); and the Edwards Aquifer (allocation of water among various users with differing short- and long-term interests, with a few spring-dependent species caught in the cross-fire). Farmers, ranchers, and loggers can be affected by ESA in various ways, depending on the particular listed species, the locale, the nature and health of the ecosystem, the ownership of the land, etc. On federal land, ESA may require land managers to restrict or modify resource uses to protect listed species; on private land, ESA prohibits takings and requires agencies providing any Federal service — such as permitting, increasing irrigation flows, or loans — to ensure the action will not adversely affect critical habitat.