Justice Stevens delivered the opinion of the Court.
The question presented is whether a moratorium on development imposed during the process of devising a comprehensive land-use plan constitutes a per se taking of property requiring compensation under the Takings Clause of the United States Constitution. This case actually involves two moratoria ordered by respondent Tahoe Regional Planning Agency (TRPA) to maintain the status quo while studying the impact of development on Lake Tahoe and designing a strategy for environmentally sound growth. The first, Ordinance 81—5, was effective from August 24, 1981, until August 26, 1983, whereas the second more restrictive Resolution 83—21 was in effect from August 27, 1983, until April 25, 1984. As a result of these two directives, virtually all development on a substantial portion of the property subject to TRPA’s jurisdiction was prohibited for a period of 32 months. Although the question we decide relates only to that 32-month period, a brief description of the events leading up to the moratoria and a comment on the two permanent plans that TRPA adopted thereafter will clarify the narrow scope of our holding.
I
The relevant facts are undisputed. The Court of Appeals, while reversing the District Court on a question of law, accepted all of its findings of fact, and no party challenges those findings. All agree that Lake Tahoe is “uniquely beautiful,” 34 F. Supp. 2d 1226, 1230 (Nev. 1999), that President Clinton was right to call it a “ ‘national treasure that must be protected and preserved,’ ” ibid., and that Mark Twain aptly described the clarity of its waters as “ ‘not merely transparent, but dazzlingly, brilliantly so,’ ” ibid. (emphasis added) (quoting M. Twain, Roughing It 174—175 (1872)).
Lake Tahoe’s exceptional clarity is attributed to the absence of algae that obscures the waters of most other lakes. Historically, the lack of nitrogen and phosphorous, which nourish the growth of algae, has ensured the transparency of its waters. Unfortunately, the lake’s pristine state has deteriorated rapidly over the past 40 years; increased land development in the Lake Tahoe Basin (Basin) has threatened the “ ‘noble sheet of blue water’ ” beloved by Twain and countless others. 34 F. Supp., at 1230. As the District Court found, “[d]ramatic decreases in clarity first began to be noted in the 1950’s/early 1960’s, shortly after development at the lake began in earnest.” Id., at 1231. The lake’s unsurpassed beauty, it seems, is the wellspring of its undoing.
The upsurge of development in the area has caused “increased nutrient loading of the lake largely because of the increase in impervious coverage of land in the Basin resulting from that development.” Ibid.
“Impervious coverage–such as asphalt, concrete, buildings, and even packed dirt–prevents precipitation from being absorbed by the soil. Instead, the water is gathered and concentrated by such coverage. Larger amounts of water flowing off a driveway or a roof have more erosive force than scattered raindrops falling over a dispersed area–especially one covered with indigenous vegetation, which softens the impact of the raindrops themselves.” Ibid.
Given this trend, the District Court predicted that “unless the process is stopped, the lake will lose its clarity and its trademark blue color, becoming green and opaque for eternity.”
Those areas in the Basin that have steeper slopes produce more runoff; therefore, they are usually considered “high hazard” lands. Moreover, certain areas near streams or wetlands known as “Stream Environment Zones” (SEZs) are especially vulnerable to the impact of development because, in their natural state, they act as filters for much of the debris that runoff carries. Because “[t]he most obvious response to this problem … is to restrict development around the lake–especially in SEZ lands, as well as in areas already naturally prone to runoff,” id., at 1232, conservation efforts have focused on controlling growth in these high hazard areas.