By Tracy L. Barnett
For Water Today

Along its mangrove-fringed shallows on Mexico’s Gulf of California, shrimp, blue crab and juvenile fish find food and shelter. Bottlenose dolphins move through its waters, while pelicans, roseate spoonbills and blue-footed boobies share the bay with tens of thousands of migratory waterbirds each winter. Generations of fishing families have depended on these waters; for the Mayo-Yoreme communities surrounding the bay, Ohuira is more than livelihood and identity. It is sacred.

The larger Santa María-Topolobampo-Ohuira lagoon complex is internationally recognized as a Ramsar wetland. Yet the very characteristics that make Ohuira so productive also make it vulnerable.

It is shallow, semi-enclosed and slow to flush. That means what enters the bay can linger. And that is why a seemingly technical question — where an ammonia plant takes in and discharges its water — has become central to a 12-year environmental battle.

Read WaterToday’s earlier report from the Topolobampo blockade, here

The nearly completed GPO-Proman plant was originally designed to withdraw roughly 2,000 cubic metres of seawater an hour and return warmer, more saline water to the lagoon. Now, after escalating protests and an encampment blockade now on its 84th day, the Mexican government is proposing a significant change: redesign the plant’s water system to avoid withdrawing water directly from Ohuira Bay or returning its discharge there.

For the communities fighting the project, that raises a new question:

If engineers move the pipes, have they really removed the threat to the bay?

A bay built to hold water

Marine biologist Diana Escobedo-Urías has studied the lagoon system for more than three decades. She describes Ohuira as the largest of three connected coastal lagoons — Santa María, Topolobampo and Ohuira — covering about 125 square kilometres.

Its average depth, she said, is only about 1.5 to 2 metres, and its opening is narrow — roughly 700 metres. In coastal-lagoon terminology, she said, Ohuira is considered a “choked” lagoon: water exchange with the sea is restricted. 

“It’s a lagoon where any contaminant remains for a long time,” Escobedo-Urías said. Studies she has worked on put the residence time at around 30 days.

That matters far beyond pollution in the conventional sense. Temperature, salinity and oxygen help determine whether shrimp larvae survive, where fish feed and which parts of the lagoon remain productive. Repeatedly adding warmer, saltier water to a shallow system that exchanges slowly with the open Gulf can change those conditions.

And Ohuira is already stressed.

Escobedo-Urías has watched the lagoon shift over decades from what she describes as a moderately enriched ecosystem to one that is now eutrophic, heavily affected by nutrient loading. Agricultural wastewater from northern Sinaloa’s vast irrigation district has been one important source of that pressure.

Yet the bay continues to function as critical habitat and an important nursery ground for fish, shrimp and other species that help sustain the already besieged and biologically critical habitat of the Gulf of California.

“It is an area for breeding and feeding commercially important species,” she said — particularly shrimp, fish and crustaceans. Ohuira is also especially important for bottlenose dolphins: its shallow, relatively quiet waters are where mothers with calves are commonly found.

Her conclusion is straightforward: “What the site needs is urgent restoration, not more impacts.”

The government’s answer: move the water

That concern is precisely what Mexico’s new “Integral Plan” is attempting to address.

The ammonia plant’s original water system was already intertwined with that of a neighboring Federal Electricity Commission, or CFE, thermoelectric plant. GPO was authorized to withdraw up to roughly 2,000 cubic metres of seawater an hour from CFE’s intake canal, which draws from Ohuira, and return about 1,400 cubic metres an hour of cooling water, concentrated brine and treated wastewater through CFE’s discharge canal.

That canal is not simply neutral plumbing. The thermoelectric plant already releases large volumes of heated cooling water into the lagoon system, and environmental studies have documented its influence on local temperature and other water conditions. GPO’s own environmental assessment acknowledged existing thermal stress in the discharge area and warned that the ammonia plant would add salinity stress.

The government now proposes breaking that loop: no GPO extraction directly from Ohuira and no discharge back into the bay. But exactly how remains unresolved. Public descriptions variously refer to using CFE infrastructure or water already discharged by the thermoelectric plant, while carrying GPO’s effluent outside Ohuira.

And “outside Ohuira Bay” is not, by itself, a hydrological answer.

Where would the new intake actually be? Where would the discharge enter the marine system? At what temperature and salinity? Which currents would carry it? Could tides or seasonal circulation bring some of that water back toward Ohuira?

Those are among the questions the communities now want answered before accepting government assurances that the redesign solves the problem.

Who gets to define ‘safe’?

The government presented its plan after several rounds of talks with the Mayo-Yoreme-led ¡Aquí No! collective, including another full day of negotiations with federal officials and representatives of GPO-Proman. The proposal was unveiled after that session as a framework intended to resolve the conflict.

Collective leaders then spent a full day examining the plan with scientists and technical advisers, followed by assemblies in the four communities closest to the project.

Their answer was not approval.

Instead, they agreed to continue investigating the government proposal—while keeping the blockade in place.

The federal government has since announced three technical commissions. One will tackle precisely those unresolved questions around the water intake and discharge. The others will establish a new environmental baseline for Ohuira Bay and develop a restoration plan for the lagoon. 

Crucially, community representatives and specialists chosen by the communities themselves will participate alongside government and company experts.

The baseline study could be especially important. Escobedo-Urías says Ohuira has changed dramatically over decades of agricultural and other human impacts. Without agreement on the bay’s condition before the ammonia plant begins operating, monitoring afterward becomes much harder to interpret.

The dispute, in other words, is no longer simply over whether residents should trust the government’s science.

It is increasingly about who gets to produce the evidence.

Water is only part of the risk

Even a successful water redesign would not resolve the communities’ other central concern: industrial safety.

Engineer and researcher José Luis Luna, who previously worked in industrial automation for Pemex, points to the scale of the proposed operation: production of roughly 2,200 tonnes of ammonia per day and storage capacity of up to 75,000 tonnes.

Producing ammonia requires high temperatures and pressures and involves hydrogen as well as anhydrous ammonia, he noted.

The company’s own environmental risk assessment examined dozens of accident scenarios, several of which Escobedo-Urías says were classified within the study as unacceptable risks.

Community leaders are now demanding updated risk modeling, emergency-response plans and clear rules governing liability, compensation and penalties if commitments are violated.

That is why moving the water pipes, however significant, cannot by itself settle the argument.

For now, the pipes stay still

GPO-Proman has agreed to participate in the new technical process and continues to insist that it intends to complete the ammonia plant.

The communities have agreed to allow limited maintenance access under their observation, but construction remains halted and the encampment continues.

For Escobedo-Urías, the central question is not whether Ohuira can absorb one more impact, but whether decades of degradation should finally be reversed.

The government’s redesign may ultimately demonstrate that engineers can separate the ammonia plant from Ohuira Bay’s water system.

Or the new studies may show that in a shallow, interconnected lagoon where water can remain for weeks, the boundary between “inside” and “outside” the bay is not as simple as moving a pipe on a map.

For now, the scientists are returning to the water, the communities are staying at the table — and outside the plant gates, ¡Aquí No! Remains.

Tracy L. Barnett is an independent journalist based in Guadalajara, Mexico. She is the founder of The Esperanza Project, a bilingual magazine covering the environment, Indigenous communities and human rights in the Americas.