June 16, 2022

Environmental, Natural Resources, & Energy Law Blog

Extraordinary Authority: The Supreme Court’s Solidifying Equitable Appropriation Jurisprudence - Adam Smith


The following examines two unanimous Supreme Court decisions from 2021 concerning the federal common law doctrine of equitable apportionment of interstate waters. In Florida v. Georgia, the Supreme Court declined to apportion the waters of the Apalachicola-Chattahoochee-Flint River Basin between Florida and Georgia on the grounds that Florida had not sufficiently proved that Georgia’s overconsumption of water had caused injury to its oyster fisheries.[2] In Mississippi v. Tennessee, the Court dismissed Mississippi’s claim that Tennessee’s siphoning of water from an interstate underground aquifer was a tortious taking and suggested that equitable apportionment was the exclusive judicial remedy for the dispute.[3] Read together, these cases show the Court is solidifying the jurisprudential and policy bases for equitable apportionment and may reflect a creeping appreciation by the Court of the effects of climate change given the growing scarcity of water.


Equitable Apportionment

Equitable apportionment is the federal common law doctrine under which the Supreme Court allocates access and use rights of waters common to multiple states. The Court’s jurisprudence regarding equitable apportionment requires first that a complaining (usually downstream) state demonstrate an actual or threatened injury of serious magnitude that has been caused by the conduct of the other upstream state.[4] The state must then show that the benefits to the downstream state of an equitable apportionment substantially outweighs the harm that might result to the upstream state.[5] In determining the equitable apportionment, the Court takes into consideration the water laws of state parties, including whether the states apply the “prior appropriation” tradition common in the west where first-in-time water claims are privileged, or the “riparian” tradition common in the rest of the country, which allows each user “reasonable use” of common waters.[6] The Court is not bound by these principles, however, and seeks an “equitable apportionment without quibbling over formulas.”[7] Its ultimate analysis rests on consideration of “all relevant factors” including all physical conditions of the interstate stream as well as the use patterns and equities of the relevant parties.[8] If the Court ultimately determines an equitable apportionment of interstate waters, the state is deemed to represent the interests of all private water users within the state, and private users are precluded from exceeding the state’s total allotment.[9] The Court hears such cases under its original jurisdiction, and given the complexity of these cases, generally appoints a Special Master[10] to make initial findings and recommendations, although the Court retains responsibility for “deciding all matters.”[11]

The Supreme Court first articulated the doctrine of equitable apportionment in 1902 and invoked it again six times before 1936.[12] The Court did not have the opportunity to use it again until 1982.[13] Since 1982 the Court has taken two other cases: South Carolina v. North Carolina in 2007 and Florida v. Georgia in 2018.[14] Of the nine cases heard by the Supreme Court where equitable apportionment has been requested, the Court has only actually effectuated an apportionment in three cases.[15] This is consistent with both the high burden placed on the complaining state and the Court’s stated preference that states apportion common waters between themselves and request Congress to ratify such apportionments as an interstate compact.[16] If states in an interstate compact then have a legal dispute over the water allocation or use, the case takes a different form than equitable apportionment cases as the Court then uses contract law principles to determine the outcome.[17]


The 2021 Cases

Florida v. Georgia

In Florida v. Georgia, the Supreme Court dismissed Florida’s request for equitable apportionment on the grounds that it had not sufficiently established that Georgia’s overconsumption of water had caused it to suffer a substantial injury.[18] This case arose from a dispute regarding the waters of the Apalachicola-Chattahoochee-Flint (ACF) River Basin, a hydrological system beginning in northwest Georgia and encompassing portions of western Georgia, eastern Alabama, and Florida’s Gulf Coast.[19] Among its various uses, the ACF River Basin provides drinking water for metropolitan Atlanta, water for agricultural use in western Georgia, heating and cooling of a nuclear powerplant in southeastern Alabama, and the shellfish and shrimp industry in the western Florida panhandle.[20] An additional significant player in the dispute is the US Army Corps of Engineers which operates Buford Dam at the start of the Chattahoochee River, north of Atlanta.[21] The three states and the Corps have disputed use of the water for decades.[22] In 1997, the states signed a compact indicating their intention to “develop an equitable apportioning of the surface waters of the ACF Basin,” but the compact expired in 2003 when the states failed to reach such an agreement.[23]

In 2013, Florida filed suit against Georgia requesting that the Supreme Court make an equitable apportionment of the waters of the ACF Basin.[24] Florida alleged substantial harm in the form of the collapse of its oyster fisheries in 2012, which it asserted was the result of a decrease in flows in the Apalachicola River caused by overconsumption of water by Georgia.[25] The Special Master Report recommended dismissal of the claim on the grounds that Florida’s alleged harm was not redressable by the Court since flows to Apalachicola were subject to the Corps’ operations at Buford Dam and the Corps was not a party to the suit.[26] In 2018, in a 5-4 decision, the Supreme Court declined to dismiss the case and instead remanded to the Special Master to make specific findings regarding redressability.[27] Following extensive additional investigation, the second Special Master Report concluded that Florida had not established by “clear and convincing evidence” that the injury to its oyster fisheries was caused by alleged overconsumption in Georgia.[28] In April 2021, the Supreme Court unanimously accepted this recommendation and dismissed the case.[29]

In finding that Florida had failed to meet the first prong of the equitable apportionment analysis, the Court focused on the multiple intervening factors in the chain of causation between Florida’s substantial harm and the alleged overconsumption in Georgia.[30] Florida had asserted that overconsumption of water in Georgia had decreased flows into Apalachicola Bay, which had increased salinity in the Bay, increasing predation of oysters and decimating oyster stocks.[31] The Court was unconvinced, however, and pointed to evidence of mismanagement of oyster fisheries in Florida (overfishing and failure to reshell oyster bars) and unprecedent prolonged drought conditions as interrupting this proposed causal chain.[32] While the Court declined to opine on the cause of the harm, it indicated that Florida had failed to meet its “heavy burden” regarding causation.[33] In concluding the decision, Justice Barrett reminded all parties of their baseline responsibility to make “reasonable” use of the “increasingly scarce resource” of the ACF Basin waters.[34]

Mississippi v. Tennessee

In Mississippi v. Tennessee, announced just seven months after Florida v. Georgia, the Supreme Court faced its first equitable apportionment case regarding groundwater.[35] The Court rejected a claim by Mississippi that Tennessee’s use of water from an interstate groundwater system was a tortious taking and unanimously held that equitable apportionment was the only remedy available.[36] The case arose out of use by the city of Memphis of waters from the Middle Claiborne Aquifer, a groundwater reservoir underlying parts of Tennessee and Mississippi as well as parts of Alabama, Arkansas, Illinois, Kentucky, Louisiana, and Missouri.[37] Mississippi alleged that Memphis siphoning water from the part of the aquifer under Tennessee had increased the flow of groundwater to Tennessee from Mississippi.[38] Mississippi asserted this was a tortious taking and sought $615 million in damages from Tennessee.[39] After granting Mississippi leave to bring its suit, the Supreme Court appointed a Special Master whose report concluded that equitable apportionment was the exclusive remedy to Mississippi’s complaint, as it is the sole “federal common-law principle for disputes over interstate water,” recommending that Mississippi’s complaint be dismissed with leave to amend to request equitable apportionment.[40] The Supreme Court agreed that equitable apportionment is the exclusive remedy regarding interstate groundwater but dismissed Mississippi’s complaint without leave to amend[41].

In reaching its conclusion to extend the doctrine of equitable apportionment to groundwater, the Court surveyed applications of the doctrine to surface water, groundwater which affected surface water, and even anadromous fish that migrate through a river-system.[42] Finding that underground aquifers that underly multiple states are “sufficiently similar” to those other applications, the Court concluded that equitable apportionment would be the only remedy the Court could provide to complainants.[43] The Court also rejected Mississippi’s assertion that it had exclusive ownership of the water within its boundaries.[44]

Regarding Mississippi’s ability to amend its complaint, the Court pointed to the fact that Mississippi had not requested such leave and had in fact explicitly rejected the suggestion that the doctrine of equitable apportionment was applicable to the dispute.[45] Moreover, the Court reasoned that equitable apportionment would require consideration of evidence beyond that which was provided by the parties to the complaint in tort and might also require joinder of additional parties, such as the other states that utilize the aquifer.[46] Concluding the opinion, Chief Justice Roberts restated the burden for equitable apportionment, namely that the complaining party provide by “clear and convincing evidence some real and substantial injury or damage.”[47]



Although the decisions differ in fundamental ways—one applies the doctrine while the other expands its scope—read together, they show the Court unanimously solidifying both the jurisprudential and policy underpinnings of equitable apportionment. Both cases stand for the proposition that equal apportionment is the sole remedy for resolution of disputes between states over common waters—whether surface or groundwater—and both demonstrate that a state must make a significant showing of fact for the Court to exercise, in the words of Justice Barrett, the “extraordinary authority to control the conduct of a coequal sovereign.”[48] Implicit in this jurisprudence—and consistent with previous decisions—is the Court’s is the preference for negotiation between states over litigation and equitable apportionment. In Florida, Justice Barrett seemed to refer to this preference in her restating Georgia’s obligation to make “reasonable use” of the “increasingly scarce” waters of the Basin, suggesting the State has an obligation to its riparian neighbor.[49] In Mississippi, Chief Justice Roberts gestured to a collaborative approach in his reference to additional parties who rely on the interstate underwater reserves and through the Court’s declination to facilitate an immediate claim for equitable apportionment.[50]

Another implicit element of both cases is the effect of climate change. In Florida, the Court acknowledged that Georgia claimed that changes in flow levels into the Apalachicola River may have been caused by “climatic changes.”[51] Although the Court avoided explicitly endorsing the idea that climate change has contributed to the injury to oyster fisheries, at one point Justice Barrett stated “evidence… indicates that the unprecedented series of multiyear droughts, as well as changes in seasonal rainfall patterns, may have played a significant role” in causing the “elevated levels of salinity and predation in [Apalachicola] Bay.”[52] These comments, coupled with Justice Barrett’s recognition that water is an “increasingly scarce” resource, suggests at the very least a recognition of the challenges that climate change has already begun to pose.[53]

While there are no such direct references to climate change in Mississippi, the presence of these two potential equitable apportionment claims in the southeastern United States also points to the emerging effects of a changing climate. Should the states of either the ACF Basin or the Middle Claiborne Aquifer enter into an interstate compact, it would be the only such compact among states in that region.[54] Currently there are 26 water apportionment compacts in the United States, all of which are west of the Mississippi River.[55] This may be due in part to the region’s riparian legal tradition, which stresses reasonable use for all riparian users, rather than the prior appropriation tradition, which allocates first-in-time rights. But this difference in legal tradition is rooted in climate and geology, with prior apportionment emerging to facilitate investment in irrigation for an arid climate and riparian rules existing where water was plentiful.[56] The fact that these water claims are being brought in the southeast may be just another indicator of trouble ahead as all states—regardless of where they are or which water law they follow—begin to face serious challenges in their water supplies due to a changing climate.


[1] Adam Smith is a Judge Advocate with the United States Navy currently pursuing a LLM in Environmental Law at Lewis & Clark Law School. The opinions expressed here do represent the Department of Defense, the Department of the Navy, or any other Governmental entity.

[2]Florida v. Georgia, 141 S. Ct. 1175 (2021).

[3]Mississippi v. Tennessee, 142 S. Ct. 31 (2021).

[4] New York v. New Jersey, 356 U.S. 296, 309 (1921).

[5] Colorado v. New Mexico, 459 U.S. 176, 190 (1982).

[6] Id. at 184. See also, “The Nature of the Water Right,” 9 Powell on Real Property § 65.03 (2022)

[7] Florida v. Georgia, 128 S. Ct. 2502, 2513 (2018) quoting New Jersey v. New York, supra note 3, at 342-343.

[8] Id. at 2515, citing South Carolina v. North Carolina, 558 U.S. 256, 271 (2010); Nebraska v. Wyoming, 325 U.S. 589, 618 (1945).

[9] Lauren D. Bernadett, “Equitable Apportionment in the Supreme Court: An Overview of the Doctrine and the Factors Considered by the Supreme Court in light of Florida v. Georgia,” 29 Journal of Environmental Law and Litigation, 511 (2014) at 514.

[10] A Special Master is a subject matter expert appointed by the Court to compile a factual record in cases where the Court exercises its original jurisdiction. See “Master,” Black’s Law Dictionary, 11th Edition.

[11] Mississippi, supra note 2, citing Kansas v. Nebraska, 574 U.S. 445, 453 (2015).

[12] See Bernadett, supra note 9 at 515-17.

[13] Id.

[14] Id.

[15] Id.

[16] Florida v. Georgia, supra note 2 at 1180, Florida v. Georgia, supra note 6, at 2509.

[17] See e.g. Kansas v. Nebraska, 574 U.S. 445 (2015) (interpreting an interstate water dispute between litigant states through the language of the interstate compact).

[18] Florida v. Georgia, supra note 2 at 1178.

[19] Id. at 1178-9

[20] Id. at 1179. For background on ACF River Basin see Kathleen Rugel, “Stakeholders Reach Consensus in Troubled Waters: Apalachicola-Chattahoochee-Flint River Basin, Southeastern USA,” Case Studies in the Environment (2020).

[21] Id.

[22] Florida v. Georgia, supra note 7 at 2509-10.

[23] Id.

[24] Florida v. Georgia, supra note 2 at 1179.

[25] Id.

[26] Id.

[27] Id.

[28] Id.

[29] Id. at 1180.

[30] Id. at 1181.

[31] Id. at 1180.

[32] Id. at 1181.

[33] Id.

[34] Id. at 1183.

[35] Mississippi v. Tennessee, supra note 3 at 39.

[36] Id. at 42.

[37] Id. at 36.

[38] Id. at 37.

[39] Id. at 38.

[40] Id. at 38-9.

[41] Id. at 42.

[42] Id. at 39.

[43] Id. at 41.

[44] Id.

[45] Id.

[46] Id. at 42.

[47] Id.

[48] Florida v. Georgia, supra note 2 at 1183.

[49] Id.

[50] Mississippi v. Tennessee, supra note 3 at 42.

[51] Florida v. Georgia, supra note 2 at 1181.

[52] Id. at 1182.

[53] Id. at 1183.

[54] See “Interstate Water Resource Management Agreements and Organizations,” Interstate Council on Water Policy, December 2020, available at https://icwp.org/wp-content/uploads/2020/12/Primer_ICWP-Interstate-Water-Agreements_FINAL_12_18_2020.pdf.

[55] Id.

[56] See e.g. Burke Griggs, “Beyond Drought: Water Rights in the Age of Permanent Depletion,” 62 U. Kan. L. Rev. 1263 (2014).