Petitioner South Florida Water Management District operates a pumping facility that transfers water from a canal into a reservoir a short distance away. Respondents Miccosukee Tribe of Indians and the Friends of the Everglades brought a citizen suit under the Clean Water Act contending that the pumping facility is required to obtain a discharge permit under the National Pollutant Discharge Elimination System. The District Court agreed and granted summary judgment to respondents. A panel of the United States Court of Appeals for the Eleventh Circuit affirmed. Both the District Court and the Eleventh Circuit rested their holdings on the predicate determination that the canal and reservoir are two distinct water bodies. For the reasons explained below, we vacate and remand for further development of the factual record as to the accuracy of that determination.

The Central and South Florida Flood Control Project (Project) consists of a vast array of levees, canals, pumps, and water impoundment areas in the land between south Florida’s coastal hills and the Everglades. Historically, that land was itself part of the Everglades, and its surface and groundwater flowed south in a uniform and unchanneled sheet. Starting in the early 1900’s, however, the State began to build canals to drain the wetlands and make them suitable for cultivation. These canals proved to be a source of trouble; they lowered the water table, allowing salt water to intrude upon coastal wells, and they proved incapable of controlling flooding. Congress established the Project in 1948 to address these problems. It gave the United States Army Corps of Engineers the task of constructing a comprehensive network of levees, water storage areas, pumps, and canal improvements that would serve several simultaneous purposes, including flood protection, water conservation, and drainage. These improvements fundamentally altered the hydrology of the Everglades, changing the natural sheet flow of ground and surface water. The local sponsor and day-to-day operator of the Project is the South Florida Water Management District (District).

Five discrete elements of the Project are at issue in this case. One is a canal called ‘‘C—11.’’ C—11 collects groundwater and rainwater from a 104 square-mile area in south central Broward County. The area drained by C—11 * * * is home to 136,000 people. At the western terminus of C—11 is the second Project element at issue here: a large pump station known as ‘‘S—9.’’ When the water level in C—11 rises above a set level, S—9 begins operating and pumps water out of the canal. The water does not travel far. Sixty feet away, the pump station empties the water into a large undeveloped wetland area called ‘‘WCA— 3,’’ the third element of the Project we consider here. WCA—3 is the largest of several ‘‘water conservation areas’’ that are remnants of the original South Florida Everglades. The District impounds water in these areas to conserve fresh water that might otherwise flow directly to the ocean, and to preserve wetlands habitat. [Citation.]

Using pump stations like S—9, the District maintains the water table in WCA—3 at a level significantly higher than that in the developed lands drained by the C—11 canal to the east. Absent human intervention, that water would simply flow back east, where it would rejoin the waters of the canal and flood the populated areas of the C—11 basin. That return flow is prevented, or, more accurately, slowed, by levees that hold back the surface waters of WCA—3. Two of those levees, L—33 and L— 37, are the final two elements of the Project at issue here. The combined effect of L—33 and L—37, C—11, and S—9 is artificially to separate the C—11 basin from WCA—3; left to nature, the two areas would be a single wetland covered in an undifferentiated body of surface and ground water flowing slowly southward.

As the above description illustrates, the Project has wrought large-scale hydrologic and environmental change in South Florida, some deliberate and some accidental. Its most obvious environmental impact has been the conversion of what were once wetlands into areas suitable for human use. But the Project also has affected those areas that remain wetland ecosystems.

Rain on the western side of the L—33 and L—37 levees falls into the wetland ecosystem of WCA—3. Rain on the eastern side of the levees, on the other hand, falls on agricultural, urban, and residential land. Before it enters the C—11 canal, whether directly as surface runoff or indirectly as groundwater, that rainwater absorbs contaminants produced by human activities. The water in C—11 therefore differs chemically from that in WCA—3. Of particular interest here, C—11 water contains elevated levels of phosphorous, which is found in fertilizers used by farmers in the C—11 basin. When water from C—11 is pumped across the levees, the phosphorous it contains alters the balance of WCA—3’s ecosystem (which is naturally low in phosphorous) and stimulates the growth of algae and plants foreign to the Everglades ecosystem.

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Congress enacted the Clean Water Act (Act) in 1972. Its stated objective was ‘‘to restore and maintain the chemical, physical, and biological integrity of the Nation’s waters.’’ [Citation.] To serve those ends, the Act prohibits ‘‘the discharge of any pollutant by any person’’ unless done in compliance with some provision of the Act. [Citation.] The provision relevant to this case, [citation], establishes the National Pollutant Discharge Elimination System, or ‘‘NPDES.’’ Generally speaking, the NPDES requires dischargers to obtain permits that place limits on the type and quantity of pollutants that can be released into the Nation’s waters. The Act defines the phrase ‘‘‘discharge of a pollutant’’’ to mean ‘‘any addition of any pollutant to navigable waters from any point source.’’ [Citation.] A ‘‘‘point source,’’’ in turn, is defined as ‘‘any discernible, confined and discrete conveyance,’’ such as a pipe, ditch, channel, or tunnel, ‘‘from which pollutants are or may be discharged.’’ [Citation.]

According to the Tribe, the District cannot operate S—9 without an NPDES permit because the pump station moves phosphorous-laden water from C—11 into WCA—3. The District does not dispute that phosphorous is a pollutant, or that C—11 and WCA—3 are ‘‘navigable waters’’ within the meaning of the Act. The question, it contends, is whether the operation of the S— 9 pump constitutes the ‘‘discharge of [a] pollutant’’ within the meaning of the Act.

The parties filed cross-motions for summary judgment on the issue of whether S—9 requires an NPDES permit. The District Court granted the Tribe’s motion, reasoning as follows:

‘‘In this case an addition of pollutants exists because undisputedly water containing pollutants is being discharged through S—9 from C—11 waters into the Everglades, both of which are separate bodies of United States water with * * * different quality levels. * * * ’’ [Citation.]

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Because it believed that the water in the C—11 canal would not flow into WCA—3 without the operation of the S—9 pump station, the Court of Appeals concluded that S—9 was the cause-in-fact of the addition of pollutants to WCA—3. It accordingly affirmed the District Court’s grant of summary judgment, and held that the S—9 pump station requires an NPDES permit. We granted certiorari. [Citation.]

The District and the Federal Government * * * advance three separate arguments, any of which would, if accepted, lead to the conclusion that the S—9 pump station does not require a point source discharge permit under the NPDES program. Two of these arguments involve the application of disputed contentions of law to agreed-upon facts, while the third involves the application of agreed-upon law to disputed facts. For reasons explained below, we decline at this time to resolve all of the parties’ legal disagreements, and instead remand for further proceedings regarding their factual dispute.

In its opening brief on the merits, the District argued that the NPDES program applies to a point source ‘‘only when a pollutant originates from the point source,’’ and not when pollutants originating elsewhere merely pass through the point source. This argument mirrors the question presented in the District’s petition for certiorari: ‘‘Whether the pumping of water by a state water management agency that adds nothing to the water being pumped constitutes an ‘addition’ of a pollutant ‘from’ a point source triggering the need for a National Pollutant Discharge Elimination System permit under the Clean Water Act.’’ * * *

This initial argument is untenable, * * *. A point source is, by definition, a ‘‘discernible, confined, and discrete conveyance.’’ [Citation.] That definition makes plain that a point source need not be the original source of the pollutant; it need only convey the pollutant to ‘‘navigable waters,’’ which are, in turn, defined as ‘‘the waters of the United States.’’ [Citation.] Tellingly, the examples of ‘‘point sources’’ listed by the Act include pipes, ditches, tunnels, and conduits, objects that do not themselves generate pollutants but merely transport them. * * * We therefore reject the District’s proposed reading of the definition of ‘‘‘discharge of a pollutant’’’ * * *

* * * [W]e turn to a second argument, advanced primarily by the Government * * *. For purposes of determining whether there has been ‘‘any addition of any pollutant to navigable waters from any point source,’’ * * *, the Government contends that all the water bodies that fall within the Act’s definition of ‘‘‘navigable waters’’’ (that is, all ‘‘the waters of the United States, including the territorial seas’’) should be viewed unitarily for purposes of NPDES permitting requirements. Because the Act requires NPDES permits only when there is an addition of a pollutant ‘‘to navigable waters,’’ the Government’s approach would lead to the conclusion that such permits are not required when water from one navigable water body is discharged, unaltered, into another navigable water body. That would be true even if one water body were polluted and the other pristine, and the two would not otherwise mix. [Citation.] Under this ‘‘unitary waters’’ approach, the S—9 pump station would not need an NPDES permit.

The ‘‘unitary waters’’ argument focuses on the Act’s definition of a pollutant discharge as ‘‘any addition of any pollutant to navigable waters from any point source.’’ [Citation.] * * * It argues that Congress intended that such pollution instead would be addressed through local nonpoint source pollution programs. [Citation], which concerns nonpoint sources, directs the Environmental Protection Agency (EPA) to give States information on the evaluation and control of ‘‘pollution resulting from * * * changes in the movement, flow, or circulation of any navigable waters or ground waters, including changes caused by the construction of dams, levees, channels, causeways, or flow diversion facilities.’’

We note, however, that [citation] does not explicitly exempt nonpoint pollution sources from the NPDES program if they also fall within the ‘‘point source’’ definition. * * *

The Government also suggests that we adopt the ‘‘unitary waters’’ approach out of deference to a longstanding EPA view that the process of ‘‘transporting, impounding, and releasing navigable waters’’ cannot constitute an ‘‘‘addition’’’ of pollutants to ‘‘‘the waters of the United States.’’’ But the Government does not identify any administrative documents in which EPA has espoused that position. * * * The ‘‘unitary waters’’ approach could also conflict with current NPDES regulations. * * * The NPDES program thus appears to address the movement of pollutants among water bodies, at least at times.

Finally, the Government * * * warn[s] that affirming the Court of Appeals in this case would have significant practical consequences. If we read the Clean Water Act to require an NPDES permit for every engineered diversion of one navigable water into another, thousands of new permits might have to be issued, particularly by western States, whose water supply networks often rely on engineered transfers among various natural water bodies. * * *

Because WCA—3 and C—11 are both ‘‘navigable waters,’’ adopting the ‘‘unitary waters’’ approach would lead to the conclusion that the District may operate S—9 without an NPDES permit. But despite its relevance here, neither the District nor the Government raised the unitary waters approach before the Court of Appeals or in their briefs respecting the petition for certiorari. (The District adopted the position as its own in its reply brief on the merits.) Indeed, we are not aware of any reported case that examines the unitary waters argument in precisely the form that the Government now presents it. As a result, we decline to resolve it here. Because we find it necessary to vacate the judgment of the Court of Appeals with respect to a third argument presented by the District, the unitary waters argument will be open to the parties on remand.

In the courts below, as here, the District contended that the C—11 canal and WCA—3 impoundment area are not distinct water bodies at all, but instead are two hydrologically indistinguishable parts of a single water body. The Government agrees with the District on this point, claiming that because the C—11 canal and WCA—3 ‘‘share a unique, intimately related, hydrological association,’’ they ‘‘can appropriately be viewed, for purposes of Section 402 of the Clean Water Act, as parts of a single body of water.’’ [Citation.] The Tribe does not dispute that if C—11 and WCA—3 are simply two parts of the same water body, pumping water from one into the other cannot constitute an ‘‘addition’’ of pollutants. * * *

The record does contain information supporting the District’s view of the facts. Although C—11 and WCA— 3 are divided from one another by the L—33 and L—37 levees, that line appears to be an uncertain one. Because Everglades soil is extremely porous, water flows easily between ground and surface waters, so much so that ‘‘[g]round and surface waters are essentially the same thing.’’ C—11 and WCA—3, of course, share a common underlying aquifer. Moreover, the L—33 and L—37 levees continually leak, allowing water to escape from WCA—3. This means not only that any boundary between C—11 and WCA—3 is indistinct, but also that there is some significant mingling of the two waters; the record reveals that even without use of the S—9 pump station, water travels as both seepage and groundwater flow between the water conservation area and the C—11 basin. * * *

We do not decide here whether the District Court’s test is adequate for determining whether C—11 and WCA—3 are distinct. Instead, we hold only that the District Court applied its test prematurely. * * * The record before us leads us to believe that some factual issues remain unresolved. The District Court certainly was correct to characterize the flow through the S—9 pump station as a non-natural one, propelled as it is by diesel-fired motors against the pull of gravity. And it also appears true that if S—9 were shut down, the water in the C—11 canal might for a brief time flow east, rather than west, as it now does. But the effects of shutting down the pump might extend beyond that. The limited record before us suggests that if S—9 were shut down, the area drained by C—11 would flood quite quickly. [Citation.] That flooding might mean that C—11 would no longer be a ‘‘distinct body of navigable water,’’ [citation] but part of a larger water body extending over WCA—3 and the C— 11 basin. It also might call into question the Eleventh Circuit’s conclusion that S—9 is the cause in fact of phosphorous addition to WCA—3. Nothing in the record suggests that the District Court considered these issues when it granted summary judgment. * * *

We find that further development of the record is necessary to resolve the dispute over the validity of the distinction between C—11 and WCA—3. * * * Accordingly, the judgment of the United States Court of Appeals for the Eleventh Circuit is vacated, and the case is remanded for further proceedings consistent with this opinion.