Groundwater Depletion and Native Fish Conservation

Groundwater Depletion and Native Fish Conservation: 

Can Rio Grande Sucker (Pantosteus plebeius) Recover in a Valley Being Pumped Dry?

BACKGROUND AND EVIDENCE

The Rio Grande Sucker (Pantosteus plebeius) is a small, bottom-feeding fish native to the upper Rio Grande basin of south-central Colorado, northern New Mexico, and parts of Arizona and Mexico (Figure 1). It scrapes algae from cobble and gravel and spawns in late spring and early summer as snowmelt flows begin to drop. Rio Grande Suckers require water near 11–16 °C and clean gravel for egg laying (Rees & Miller, 2005; USFWS, 2024). Most fish reach breeding age at three or four years, and the oldest individuals recorded reached six or seven (USFWS, 2024; Rees & Miller, 2005). Young die at high rates, and strong spawning years are inconsistent, so if a stream dries during spawning or early rearing, an entire year class can be lost, depressing the population for years afterward (Rees & Miller, 2005; USFWS, 2024). Colorado listed the species as state-endangered in November 1993, and it remains endangered in the state today (Rees & Miller, 2005; CPW, 2024).

This paper focuses on the northeastern corner of the San Luis Valley in Saguache and Alamosa counties, Colorado. The valley is a high-elevation, closed-basin (endorheic) system; water flowing in has no river outlet. Snowmelt from the Sangre de Cristo and San Juan ranges recharges a shallow aquifer beneath the valley floor that once fed artesian springs, year-round creeks, and large shallow wetlands (Leonard & Watts, 1988). A few higher-elevation streams and these spring-fed surface waters hold the sucker's documented populations in Colorado (Rees & Miller, 2005; USFWS, 2024). Baca National Wildlife Refuge, a 93,000-acre federal refuge near Crestone, Colorado, is the species' main conservation site in this area; the spring-fed lower reach of Crestone Creek on the refuge supports a native Rio Grande Sucker population (USFWS, n.d.; CPW, 2023).

While conservation efforts concentrate on this northeastern corner, the extent of the problem is valley-wide. San Luis Valley farmers draw large volumes of water from the Rio Grande for irrigation, cutting into the flow that Colorado must send downstream to New Mexico and Texas under the Rio Grande Compact of 1939. To cover that shortfall, the federal Closed Basin Project, authorized by Congress in 1972 and run by the Bureau of Reclamation, pumps groundwater from the northern valley’s endorheic basin and moves it through a 42-mile channel to the Rio Grande (RGWCD, n.d.). The project creates a direct trade-off: for every acre-foot pumped and delivered to the river, valley farmers keep an acre-foot of the Rio Grande’s water they would otherwise surrender (RGWCEI, 2012). In effect, the project pumps the same groundwater that feeds the Rio Grande Sucker habitat, allowing farmers to keep irrigating with river water. On top of that, aquifer-fed irrigation across about 600,000 acres of farmland, the valley's main economic driver, pulls directly from the same aquifer (Water Education Colorado, 2013). Both uses draw down the shallow groundwater that supports surface waters across the valley floor.

The shallow aquifer has lost more than one million acre-feet since 2002, a result of long-term drought and heavy pumping (Water Education Colorado, 2020). The Closed Basin Project was built to deliver up to 100,000 acre-feet of water to the Rio Grande each year, but it has never come close to that target. Since 2000, it has averaged about 17,000 acre-feet per year, and of its 170 wells, roughly 60 are shut off because groundwater dropped too far, and another 11 are offline because their water is too salty to legally return to the river (RGWCEI, 2012; RGWCD, n.d.). That shortfall measures how far the aquifer has fallen, and it is the same aquifer that keeps surface water flowing on the valley floor.

The effects on the sucker’s habitat are pronounced. Many year-round artesian springs that once fed creeks and wetlands have shrunk or dried as groundwater dropped, and shallow wetlands at Baca NWR now fill only briefly during wet springs or heavy summer rain (Water Education Colorado, 2020; USFWS, n.d.). USGS sensors in use from 2016 to 2019 documented repeated drying of valley-floor creeks (USGS, 2020). Suckers persist where a reach dries only part of the time, but a reach that goes fully dry loses its population (USFWS, 2024). As habitat shrinks, remaining fish are pushed into smaller, isolated pockets, and McPhee et al. (2008) linked that isolation to reduced genetic diversity. The invasive White Sucker (Catostomus commersonii) competes with the Rio Grande Sucker for food and habitat, and where it is present, Rio Grande Sucker numbers decline (McPhee, 2007; Rees & Miller, 2005). The 2024 USFWS Species Status Assessment identified water loss from diversions and groundwater pumping, and invasive species, as primary threats to the sucker's persistence (USFWS, 2024). While wildfire can degrade habitat through post-fire erosion and sedimentation, the assessment notes it has little direct impact on the species itself, and none of the 32 populations face high wildfire risk in the 10-year outlook (USFWS, 2024). 

The same groundwater decline threatening Rio Grande Suckers also strains the farm economy. Hundreds of irrigation wells have already been weakened or failed, and hundreds more are at risk of being shut off if the aquifer is not restored to required levels by 2031 (Water Education Colorado, 2020). Fish and farmers are losing ground to the same problem.

The main conservation success has been a state-led recovery effort launched with the 1994 Rio Grande Sucker Recovery Plan (Rees & Miller, 2005), carried out mostly through CPW's captive breeding and reintroduction program (CPW, 2024). By 1994, the species was down to a single Colorado population of about 1,500 fish in a 3.7-mile reach of Hot Creek (Rees & Miller, 2005). Since 2002, the John W. Mumma Native Aquatic Species Restoration Facility in Alamosa has released nearly 450,000 suckers into 20 waters, and Colorado now has eight established populations (CPW, 2024). In 2023, CPW, the USFWS, and the National Park Service moved chub and sucker from a drying Crestone Creek to spring-fed Big Spring Creek in Great Sand Dunes National Park, about 20 miles south of the refuge, to establish a new population (CPW, 2023). A 2018 Conservation Agreement among twelve partners and a 2021 Conservation Strategy helped support the June 2024 USFWS decision not to list the species (CPW, 2024; USFWS, 2024). 

Groundwater management has fared worse. Subdistrict 1, the largest of the seven groundwater management districts the Rio Grande Water Conservation District oversees on the valley floor, adopted a fee-based plan in 2011, paying farmers to fallow fields so the aquifer could recover; by 2017 irrigators had returned about 350,000 acre-feet, roughly half of what they owed, but the 2018 drought erased about 70% of those gains in one season (Water Education Colorado, 2020). The Closed Basin Project itself has no legal requirement to protect aquatic species that depend on the groundwater it pumps; under its 1972 authorization, compact delivery comes first (RGWCD, n.d.). Colorado has also granted no instream flow rights to protect the valley-floor creeks and springs where suckers live outside the refuge, so no legal tool keeps those streams wet as the aquifer falls.

Several data gaps cloud predictions of conservation success. The largest uncertainty is attribution: no one can yet separate how much valley-floor drying results from pumping versus reduced snowpack and drought, because both occur together, and little pre-pumping record exists (Leonard & Watts, 1988). A second question is whether restoring the aquifer to its 2031 target would restore year-round flow, or whether the system has crossed a threshold it cannot fully recover from. A third is biological: USFWS (2024) notes that no one has defined how much flow or what water quality the sucker actually needs, so no aquifer target can be matched to fish habitat with confidence. Finally, it is unclear whether stocking can sustain populations in the long term if flows continue to decline. Putting fish into a drying habitat buys time; it is not recovery.

HUMAN DIMENSIONS OF THE PROBLEM

Rio Grande Sucker conservation in the San Luis Valley comes down to who gets to use the water. The shallow aquifer that feeds the creeks the suckers need also supports the irrigation that drives the regional farm economy, and current law offers no single route for reconciling these competing interests.

Subdistrict 1 covers about 3,000 irrigation wells across Alamosa and parts of Rio Grande and Saguache counties (Alamosa News, 2022; Colorado Sun, 2021). Its members pay a fee on every acre-foot pumped, which funds payments to fallow fields; the fee climbed from $75 to $150 an acre-foot over the program's first decade, and in early 2024 the district approved raising it to $500, a level that faces a court challenge and could take effect as soon as 2026 (Big Pivots, 2024; Alamosa Citizen, 2025). Habitat protection is not part of its mandate. The Colorado Division of Water Resources, led by the State Engineer, regulates pumping under a 2004 statute requiring the aquifer to reach a sustainable level by 2031, and it holds authority to shut down all 3,000 Subdistrict 1 wells if recovery stalls (Water Education Colorado, 2020; Colorado Sun, 2021). Colorado Parks and Wildlife runs the sucker recovery program but does not regulate groundwater, and without instream flow rights off the refuge, it depends on voluntary cooperation from water users (CPW, 2024). The U.S. Fish and Wildlife Service manages Baca NWR but has no authority over the off-refuge pumping that is drying its creeks, and the Bureau of Reclamation runs the Closed Basin Project under the same mandate: its mission is compact compliance, not species protection.

Two other groups shape the politics. Acequia parciantes, members of community-governed ditch associations, hold the state's oldest water rights; the People's Ditch in San Luis, decreed in 1852, is the first water right in Colorado, and acequia governance treats water as a shared community resource rather than private property, at odds with prior appropriation (Colorado Politics, 2023; Colorado Water Trust, 2022). Front Range water exporters apply a new pressure: Renewable Water Resources has proposed buying valley farmland and piping about 22,000 acre-feet per year to Denver suburbs, drawing broad local opposition from agricultural, municipal, and conservation groups alike (Colorado Sun, 2021; Alamosa News, 2019a, 2019b).

Five overlapping frameworks govern valley water: the Rio Grande Compact of 1939; the 1972 Closed Basin Project authorization; Colorado's prior appropriation doctrine; the 2004 sustainability statute and its 2031 target; and the 2018 Conservation Agreement with its 2021 Conservation Strategy. Four were not written with the species in mind, and the one that was sets no enforceable pumping limits (CPW, 2024; USFWS, 2024).

Two policy gaps matter most. First, Colorado has not granted instream flow water rights to protect surface flows in the valley-floor creeks and springs outside Baca NWR. Without those rights, prior appropriation provides no legal basis to require that water remain in those streams when senior agricultural rights are exercised. Second, the 2024 USFWS decision not to list the species under the Endangered Species Act removed the federal mechanism that would have required Section 7 consultation for federal actions affecting listed species, including continued operation of the Closed Basin Project (USFWS, 2024).

Stakeholders read these frameworks differently. CPW frames the agreements and the non-listing decision as proof that voluntary collaboration works, while Subdistrict 1 farmers treat the 2031 target primarily as a regulatory threat and join fee programs to keep regulators from shutting off their wells, rather than as a conservation goal (CPW, 2024; Alamosa News, 2022). Some local managers go further and dispute that aquifer decline threatens compact compliance at all, arguing the closed basin interacts little with the Rio Grande (Cotten et al., 2024).

The human stakes are concentrated and unequal. A 2025 study for American Rivers estimated that water-dependent activity supports $4.5 billion in annual output across the six valley counties, with irrigated crop farming alone producing $310.3 million in direct output and valley agriculture making up 39% of Colorado's farm output, even though the region holds under 1% of the state's population (American Rivers, 2025). The valley is also poor: median household income is $71,600 compared with $92,900 statewide, and 15% of residents live below the poverty line compared with 9.3% statewide (American Rivers, 2025). The counties most dependent on agriculture tend to be the poorest, which is why even small cuts to pumping threaten jobs and incomes and why agricultural stakeholders resist restrictions (Alamosa Citizen, 2025).

The deadlock here is partly structural and partly cognitive. Authority over the problem is fragmented across agencies that each control one piece and answer to different constituencies, a pattern Yaffee (1997) identifies as a recurring source of piecemeal solutions and diminished accountability in environmental policy: the district manages pumping, the State Engineer enforces the compact, CPW manages the fish, and the Bureau of Reclamation runs the project, with no single body accountable for the creeks. Fragmented authority also makes political action costly, because nearly any move costs some stakeholder's support, so elected officials default to the status quo (Yaffee, 1997). 

Several predictable decision biases reinforce that default. Stakeholders tend to frame the choice as fish versus farms, which Bazerman (2007) calls the fixed-pie bias: a false-choice dichotomy that assumes a gain for one side must be a loss for the other. Omission bias compounds it; people accept harm resulting from inaction more readily than the equivalent harm they would have to cause by acting (Bazerman, 2007), so allowing the sucker to slip toward extirpation through continued pumping feels less culpable than enacting a rule that visibly costs farmers water. Finally, the genuine scientific uncertainty about how much drying comes from pumping becomes an argument for waiting, even though delay is itself a choice with consequences; Ludwig et al. (1993) warn that calls for more study before acting often function as delaying tactics and that effective policy must instead confront uncertainty directly.

Public discussion centers on three contested questions: who is responsible for the aquifer drawdown, who should bear the cost of recovery, and whether the recovery target is even attainable under the current climate. The species itself is not the controversial part. The controversy is over whether groundwater management should be tightened specifically to protect aquatic habitat. Conservation and acequia groups argue that habitat, water rights, and cultural survival are inseparable (Colorado Open Lands, 2023), while farmers, facing a 2031 target they doubt they can meet, resist any added limits (Alamosa Citizen, 2025). Front Range export threats briefly unite these camps, since agricultural, acequia, and conservation interests all oppose sending valley water to Denver (Colorado Sun, 2021; Tory, 2021). Across regional coverage, the agricultural and legal stakes dominate, while the sucker's needs, well documented in agency reports, remain largely absent from the debate that will decide their fate.

MANAGEMENT OR POLICY ALTERNATIVES

Four realistic options span the range from no change to shutting the Closed Basin Project down completely.

Alternative 1: Status Quo. Keep current policy. Subdistrict 1 works toward its 2031 aquifer target through pumping fees, and the Closed Basin Project continues to operate under its 1972 authorization. No new action is required, and the State Engineer retains authority to shut down all 3,000 Subdistrict 1 wells if the target slips (Colorado Sun, 2021; Big Pivots, 2024). Success is measured by the aquifer index, which says nothing about fish. The probability of sucker recovery is low: the 2018 drought erased about 70% of early aquifer gains, and the project has no legal requirement to protect aquatic species (Water Education Colorado, 2020; RGWCD, n.d.). The key uncertainty is whether voluntary aquifer work can restore streamflow before the sucker population falls past the point of recovery. CPW reads the 2024 non-listing decision as proof that the approach works (CPW, 2024), while irrigators see anything beyond the 2031 target as a threat to the farm economy (Alamosa Citizen, 2025).

Alternative 2: Voluntary Water Leasing for Ecological Flows. Enroll farmers in a leasing program that they join by choice, paying them to leave water in the system. The program cannot compel anyone to lease; the payment is the incentive that makes participation worth a farmer's while, the same approach Subdistrict 1 already uses when its fee revenue pays irrigators who choose to fallow fields (Water Education Colorado, 2020; Alamosa News, 2022). The difference: outside funding and a different destination. Funding comes from CPW, USDA Farm Bill conservation programs, and the USFWS Partners for Fish and Wildlife Program, rather than irrigator fees, and leased water stays in occupied sucker creeks during the late spring and early summer spawning period, not just in the aquifer. This option needs a legal path to hold leased water in the creek, because without an instream flow right, a downstream user can divert it; leasing to CPW or the Colorado Water Trust, or targeting ranches sitting directly on occupied creeks, solves that. Success means higher low flows and stable or improving CPW surveys. Probability is moderate, and the participation rate is the main source of uncertainty. Sieg et al. (2009) found that voluntary non-lead ammunition programs in Arizona reached over 80% compliance from hunters, but lead exposure rates in condors indicated that even that level fell short of self-sustaining recovery. The same risk applies here: partial flow restoration may only hold suckers at low numbers. Farmers prefer incentive-based programs over regulation, but enrollment depends on lease prices that compete with farm income (American Rivers, 2025).

Alternative 3: Petition for ESA Listing with Section 7 Consultation. Seek renewed federal listing after the 2024 non-listing decision, submitting updated evidence on aquifer-driven habitat loss to trigger a new 90-day finding and 12-month review (USFWS, 2024). Listing would force the Bureau of Reclamation to undergo Section 7 consultation on Closed Basin Project operations, restoring the federal mechanism that non-listing removed. Success means a recovery plan with quantitative flow and population targets and an enforceable biological opinion, tracked through CPW surveys and USGS gauges (USGS, 2020). Probability is moderate to high if USFWS lists, because this option imposes legal duties rather than incentives, but enforcement is uncertain: USFWS may again decline, or the resulting biological opinion may not impose hard limits on pumping. CPW and USFWS field staff likely support a renewed petition, while the district, irrigators, and the congressional delegation frame federal regulation as a threat to the farm economy (CPW, 2024; Alamosa Citizen, 2025).

Alternative 4: Closure of the Closed Basin Project. Deauthorize and shut the project down. Congress designed its 170 wells to deliver up to 100,000 acre-feet per year, but the average delivery since 2000 is about 17,000 acre-feet per year, with roughly 60 wells offline due to low groundwater and 11 due to salinity (RGWCEI, 2012; RGWCD, n.d.). Closure removes a major driver of drawdown but would require an act of Congress, ideally phased over several years to soften the shock. Success means a recovering shallow aquifer, restored tributary base flows, and sucker populations above CPW's recovery threshold, tracked by USGS monitoring and CPW surveys. The biological probability ranks highest; the political probability ranks lowest. Economic fallout is the main uncertainty, since water-dependent activity supports $4.5 billion in annual output across the six counties (American Rivers, 2025). USFWS and CPW are likely the only supporters; the district, irrigators, and delegation oppose closure.

RECOMMENDATIONS

I recommend Alternative 2, voluntary water leasing for ecological flows, as the primary near-term action, paired with two changes that the leasing program alone cannot supply. The evidence points here for three reasons. The status quo (Alternative 1) measures success by an aquifer index that says nothing about fish and has already shown it can lose 70% of its gains in a single drought. Closure (Alternative 4) is the strongest biological option but the weakest political one, asking a region where water-dependent activity supports $4.5 billion in annual output and 39% of Colorado's farm output to absorb a shock Congress is unlikely to impose. Leasing works within the collaborative approach the valley already trusts, it targets the spring spawning window when flow matters most, and it can draw on existing state and federal funding.

Leasing is also the alternative that breaks the fish-versus-farms framing rather than reinforcing it. Paying willing farmers to leave water in occupied creeks turns a contested allocation into a transaction both sides gain from, the kind of wise tradeoff Bazerman (2007) describes as the way out of a fixed-pie standoff, and the superordinate goal Yaffee (1997) recommends for fragmented disputes: keeping water in the streams while keeping money in the farm economy. It is firm on the end, recovering the sucker's flows, but flexible on the means, leaving each farmer's participation a voluntary choice.

This alternative protects fish only if the leased water actually stays in the creek, so the recommendation rests on two paired steps. First, Colorado Parks and Wildlife or the Colorado Water Trust should secure instream flow rights for the specific occupied reaches, closing the legal gap that now allows downstream users to divert any water a farmer leaves behind. Second, because no one has yet defined how much flow or what water quality the sucker needs (USFWS, 2024), the program should begin as a pilot on two or three occupied creeks near Baca National Wildlife Refuge, using the USGS temperature and intermittency sensors already deployed there (USGS, 2020) together with annual CPW population surveys to set minimum flow targets and test whether leasing holds them.

The pilot should run on a fixed schedule with a clear escalation trigger: if flows and populations do not stabilize within five years, the renewed ESA petition in Alternative 3 becomes the backstop, using the threat of federal Section 7 review to bring reluctant water users to the table. Voluntary leasing buys the valley time to protect its fish without breaking its farms, but only if the law keeps the water in the stream.

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