The Mexican Water Treaty of 1944 committed the U.S. to deliver
1.5 million acre-feet of water to Mexico on an annual basis, plus
an additional 200,000 acre-feet under surplus conditions. The
treaty is overseen by the International Boundary and Water
Commission.
Colorado River water is delivered to Mexico at Morelos Dam,
located 1.1 miles downstream from where the California-Baja
California land boundary intersects the river. The river’s
natural terminus is the Gulf of California in Mexico, but because
of the dams and diversion facilities throughout the Colorado
River Basin, natural flow rarely reaches the Gulf. Water diverted
at Morelos Dam is primarily used to irrigate Mexicali Valley
farmland, and also supplies the cities of Mexicali, Tecate and
Tijuana.
After the thirtieth consecutive month without rain, the
townsfolk of San Francisco de Conchos in the northern Mexican
state of Chihuahua gather to plead for divine intervention. …
Under the terms of a 1944 water-sharing agreement, Mexico must
send 430 million cubic metres of water per year from the Rio
Grande to the US. … Following pressure from Republican
lawmakers in Texas, the Trump administration warned Mexico that
water could be withheld from the Colorado
River unless it fulfils its obligations under the
81-year-old treaty. … Since then, Mexico has transferred
an initial 75 million cubic metres of water to the US via their
shared dam, Amistad, located along the border, but that is just
a fraction of the roughly 1.5 billion cubic metres of Mexico’s
outstanding debt. … Farmers on the Mexican side read the
agreement differently. They say it only binds them to send
water north when Mexico can satisfy its own needs, and argue
that Chihuahua’s ongoing drought means there’s no excess
available.
… The odor comes from a toxic gas that’s colorless and smells
like rotten eggs. It’s hydrogen sulfide, or H2S, a byproduct of
the millions of gallons of untreated sewage from Mexico that
regularly chokes one of America’s most endangered rivers, the
Tijuana River. UC San Diego researchers,
led by Kim Prather, recently found that sewage-linked bacteria
and toxic chemicals in the river are airborne. In the past
couple of years, the volume of sewage flows, laced with
contaminated stormwater, noxious chemicals and trash, has been
the highest in the last quarter-century, worsening conditions
for those living and working nearby. … But the data remains
woefully insufficient to conclude what long-term exposure means
for individuals, especially for vulnerable groups such as
children or those with respiratory problems. And there are only
three monitors generating information for a border region that
is home to tens of thousands of residents who have raised
concerns for years.
Several California state assembly memebers are asking President
Trump to declare a state of emergency as a way to quickly
mitigate sewage pollution that for decades has been tainting
the Tijuana River Valley just north of the border. On Tuesday
morning, legislation known as AJR 16, received unanimous
support in the Assembly’s Environmental Safety and Toxic
Materials Committee. Assemblymember David Alvarez, one of
the sponsors, says Trump needs to take action to address the
“environmental injustice facing communities, which have endured
beach closures, air and water contamination, and diminished
economic activity.” … According to his office, more than
200 billion gallons of toxic wastewater have flowed into
California from Mexico along the Tijuana River since
2018. AJR 16 also takes into account the New River that
runs through the city of Calexico in the Imperial Valley. For
years, this waterway has been polluted with industrial waste,
urban runoff, chemicals and fertilizers that originated south
of the border.
San Diego County leaders are committing the county to stepping
up efforts to help residents bearing the brunt of the
decades-long Tijuana River sewage crisis. On Tuesday, the Board
of Supervisors voted 3-1 to explore what it would take to
administer a plan that calls for further monitoring and
mitigation of cross-border pollution from Mexico and
implementing health protections. The plan, proposed by Imperial
Beach Mayor Paloma Aguirre and brought before the board by
Supervisor Terra Lawson-Remer, consists of five key elements:
study the health impacts of chronic exposure to the toxic sewer
gas hydrogen sulfide; assess the full scope of crisis-linked
economic losses; eliminate a hot spot along the Tijuana River
to lessen aerosolization of the gas; and create a county sewage
crisis chief position. It also suggests giving schools and
child care centers air filtration that’s engineered to remove
hydrogen sulfide from the air if the county can show that the
infrastructure will effectively eliminate odors.
… The state Senate passed two bills by Sen. Steve Padilla
aimed at protecting the polluted Tijuana River
Valley. One would authorize using funds from the
new East Otay Mesa toll road for the South Bay International
Boundary and Water Commission sewage treatment facility, which
filters sewage from Mexico and discharges the treated water to
the Pacific Ocean. The other would prohibit a state agency
from approving a new landfill, until the local agency that
oversees waste facilities has held a public hearing on the
project and certified that it won’t harm an environmentally
burdened community. It’s aimed at the East Otay Mesa Recycling
Collection Center and Landfill, which was passed by ballot
measure 15 years ago. This is Padilla’s second stab at
this issue. Last year he proposed a related bill that would
have prohibited a regional water board from issuing a waste
discharge permit for a new landfill in the Tijuana River
Valley. That bill failed on the Assembly floor, but
Padilla is trying again.
The design-build team of Stantec and PCL Construction detailed
the planned $250-million expansion of the South Bay
International Wastewater Treatment Plant in San Diego, Calif.,
a project that has recently been fast-tracked due to the
ongoing transboundary raw sewage flows from Tijuana,
Mexico. Michael Watson, senior vice president and major
projects lead for water at Stantec and Jeff Newman, operations
manager at PCL, said at a public meeting held by the U.S.
section of the International Boundary and Water Commission June
12 that they had validated that 50 million gallons per day can
be treated by the plant after the expansion and will soon put
out early work packages. … New IBWC U.S. Commissioner
Chad McIntosh told local officials and attendees at the forum
that even after the expansion they would continue to press
Mexico to halt the cross-boundary sewage and chemical flows
into the Tijuana River which eventually flow
into the Pacific Ocean near the South Bay community of Imperial
Beach.
President Donald Trump recently addressed Mexico’s failure to
pay the water it owes the U.S. under a decades-old treaty.
Under the 1944 treaty, Mexico must send 1.75 million acre-feet
of water to the U.S. from the Rio Grande every five years, and
the United States is to pay Mexico 1.5 million acre-feet of
water annually via the Colorado River out West. Mexico,
however, has fallen behind on its payments. … The water
payments are just one of several water-related issues at which
the U.S. and Mexico are at odds. In San Diego, raw sewage has
been flowing in from Mexico for decades via the Tijuana River,
which runs from the south to the north. When it rains, tons of
debris and trash, in addition to millions of gallons of
sewage-tainted water, make their way north of the border and,
eventually, into the Pacific Ocean. The bacteria in the water
has forced the closure of beaches in southern San Diego that
have already been in place for years.
… Trump has found a perhaps obvious avenue to pursue his goal
to ensure the United States is getting a fair shake on the
world stage. But some experts fear bringing tariff threats and
“America First” rhetoric into the world of water negotiations
will backfire, and that the careful work of administering the
1944 water treaty could get damaged in the process.
… The treaty is a complex document, but it requires the
United States to deliver water from the Colorado River to
Mexico, and Mexico to deliver water from the Rio Grande to the
United States. … After Trump threatened tariffs in
April, Mexico’s president did announce an additional water
shipment to Texas from Mexico’s reservoirs on the Rio Grande.
But experts say there just isn’t enough water available for
Mexico to get back on track by October. … Many of
northern Mexico’s reservoirs are low or empty, and in some
places, a lack of rain means rivers run dry.
During the first semiannual meeting of the North American
Development Bank (NADBank) in 2025, the Governments of the
United States and Mexico, through the Board of
Directors, agreed to invest up to US$400 million in
priority water conservation and diversification infrastructure
in response to prolonged drought conditions throughout the
U.S.-Mexico border region. NADBank will welcome input from the
public on the Water Resilience Fund (WRF) during a 30-day
public comment period, after which the Board will consider its
final approval. Through the WRF, NADBank will allocate up
to US$100 million in retained earnings over the next five years
for concessional financing, as well as make up to US$300
million available for low-interest loans from its established
lending resources. NADBank may also supplement these
instruments with market-rate financing to further expand the
reach and impact of available resources.
Latin America is at a pivotal moment in its water
infrastructure development. Historically hindered by limited
public funding and rigid policies, investment in sanitation,
wastewater treatment, and desalination is now gaining momentum
due to population growth, climate pressures, and rising
industrial demand. Chile, Peru, Brazil, and Mexico are at the
forefront of this shift, each driven by unique socio-economic
needs. … Mexico faces severe water
scarcity due to droughts, air pollution, and structural
challenges, particularly in northern states like Chihuahua,
Sonora, Sinaloa, and Baja California. Financial constraints
have further hampered efforts to address the crisis. … In
April 2025, the government also announced a US$1.5 billion
investment for 37 water infrastructure projects, focusing on
irrigation, hydro agriculture, and potable water improvements.
Key projects include a desalination plant in
Rosarito, Baja California, and aqueducts in Colima and
Veracruz.
A cross-border sewage crisis affecting Southern California
could play a role in a prominent congressional race, where a
Republican challenger has become a national figure on the
issue. Jim Desmond, a San Diego County supervisor, has been
sounding the alarm recently on Fox News and other conservative
outlets about the untreated sewage that’s been flowing from the
Tijuana River in Mexico to the Pacific Ocean, contaminating the
water and sickening residents. At the same time, he’s seeking
to unseat Rep. Mike Levin, accusing the Democratic incumbent of
not doing enough to protect residents. … Desmond says
Levin’s focus — including $635 million that Levin has gotten
approved for projects like improving a major sewage plant on
the Mexican side through the bipartisan infrastructure law,
among other actions — lets Mexican officials off the hook.
The San Diego County Board of Supervisors approved a resolution
Wednesday that urges the federal government to pressure Mexico
to end the Tijuana River sewage crisis. The resolution, brought
forth by Republican Supervisor Jim Desmond, passed by a vote of
3-1. But it was Desmond who ultimately cast the lone “no” vote
because the amended version officials approved doesn’t go far
enough, he said. … Specifically, the resolution calls on
Congress to pass legislation that would hold Mexico accountable
for failing to prevent sewage from polluting communities in the
county’s southwest region. Some measures suggested include
federal authorization to divert or restrict the Tijuana River
temporarily in south San Diego. It also urges curtailing the
export of potable water to Tijuana or limiting cross-border
activity at U.S. ports of entry during sewage-linked
emergencies that the county declares.
Learn the history and challenges facing the West’s most dramatic
and developed river.
The Layperson’s Guide to the Colorado River Basin introduces the
1,450-mile river that sustains 40 million people and millions of
acres of farmland spanning seven states and parts of northern
Mexico.
The 28-page primer explains how the river’s water is shared and
managed as the Southwest transitions to a hotter and drier
climate.
Martha Guzman recalls those awful
days working on water and other issues as a deputy legislative
secretary for then-Gov. Jerry Brown. California was mired in a
recession and the state’s finances were deep in the red. Parks
were cut, schools were cut, programs were cut to try to balance a
troubled state budget in what she remembers as “that terrible
time.”
She now finds herself in a strikingly different position: As
administrator of the U.S. Environmental Protection Agency’s
Region 9, she has a mandate to address water challenges across
California, Nevada, Arizona and Hawaii and $1 billion to help pay
for it. It is the kind of funding, she said, that is usually
spread out over a decade. Guzman called it the “absolutely
greatest opportunity.”
Water is flowing once again
to the Colorado River’s delta in Mexico, a vast region that
was once a natural splendor before the iconic Western river was
dammed and diverted at the turn of the last century, essentially
turning the delta into a desert.
In 2012, the idea emerged that water could be intentionally sent
down the river to inundate the delta floodplain and regenerate
native cottonwood and willow trees, even in an overallocated
river system. Ultimately, dedicated flows of river water were
brokered under cooperative
efforts by the U.S. and Mexican governments.
For the bulk of her career, Jayne
Harkins has devoted her energy to issues associated with the
management of the Colorado River, both with the U.S. Bureau of
Reclamation and with the Colorado River Commission of Nevada.
Now her career is taking a different direction. Harkins, 58, was
appointed by President Trump last August to take the helm of the
United States section of the U.S.-Mexico agency that oversees
myriad water matters between the two countries as they seek to
sustainably manage the supply and water quality of the Colorado
River, including its once-thriving Delta in Mexico, and other
rivers the two countries share. She is the first woman to be
named the U.S. Commissioner of the International Boundary and
Water Commission for either the United States or Mexico in the
commission’s 129-year history.
Nowhere is the domino effect in
Western water policy played out more than on the Colorado River,
and specifically when it involves the Lower Basin states of
California, Nevada and Arizona. We are seeing that play out now
as the three states strive to forge a Drought Contingency Plan.
Yet that plan can’t be finalized until Arizona finds a unifying
voice between its major water players, an effort you can read
more about in the latest in-depth article of Western Water.
Even then, there are some issues to resolve just within
California.
It’s high-stakes time in Arizona. The state that depends on the
Colorado River to help supply its cities and farms — and is
first in line to absorb a shortage — is seeking a unified plan
for water supply management to join its Lower Basin neighbors,
California and Nevada, in a coordinated plan to preserve water
levels in Lake Mead before
they run too low.
If the lake’s elevation falls below 1,075 feet above sea level,
the secretary of the Interior would declare a shortage and
Arizona’s deliveries of Colorado River water would be reduced by
320,000 acre-feet. Arizona says that’s enough to serve about 1
million households in one year.
The Colorado River Delta once spanned nearly 2 million acres and
stretched from the northern tip of the Gulf of California in
Mexico to Southern California’s Salton Sea. Today it’s one-tenth
that size, yet still an important estuary, wildlife habitat and
farming region even though Colorado River flows rarely reach the
sea.
This issue of Western Water examines the ongoing effort
between the United States and Mexico to develop a
new agreement to the 1944 Treaty that will continue the
binational cooperation on constructing Colorado River
infrastructure, storing water in Lake Mead and providing instream
flows for the Colorado River Delta.
As vital as the Colorado River is to the United States and
Mexico, so is the ongoing process by which the two countries
develop unique agreements to better manage the river and balance
future competing needs.
The prospect is challenging. The river is over allocated as urban
areas and farmers seek to stretch every drop of their respective
supplies. Since a historic treaty between the two countries was
signed in 1944, the United States and Mexico have periodically
added a series of arrangements to the treaty called minutes that
aim to strengthen the binational ties while addressing important
water supply, water quality and environmental concerns.
California’s little-known New River has been called one of North
America’s most polluted. A closer look reveals the New River is
full of ironic twists: its pollution has long defied cleanup, yet
even in its degraded condition, the river is important to the
border economies of Mexicali and the Imperial Valley and a
lifeline that helps sustain the fragile Salton Sea ecosystem.
Now, after decades of inertia on its pollution problems, the New
River has emerged as an important test of binational cooperation
on border water issues. These issues were profiled in the 2004
PBS documentary Two Sides of a River.
Redesigned in 2017, this beautiful map depicts the seven
Western states that share the Colorado River with Mexico. The
Colorado River supplies water to nearly 40 million people in
Arizona, California, Colorado, Nevada, New Mexico, Utah, Wyoming
and Mexico. Text on this beautiful, 24×36-inch map, which is
suitable for framing, explains the river’s apportionment, history
and the need to adapt its management for urban growth and
expected climate change impacts.
As part of the historic Colorado
River Delta, the Salton Sea regularly filled and dried for
thousands of years due to its elevation of 237 feet below
sea level.
The most recent version of the Salton Sea was formed in 1905 when
the Colorado River broke
through a series of dikes and flooded the seabed for two years,
creating California’s largest inland body of water. The
Salton Sea, which is saltier than the Pacific Ocean, includes 130
miles of shoreline and is larger than Lake Tahoe.
The Mexican Water Treaty of 1944 committed the U.S. to deliver
1.5 million acre-feet of water to Mexico on an annual basis, plus
an additional 200,000 acre-feet under surplus conditions. The
treaty is overseen by the International Boundary and Water
Commission.
Colorado River water is delivered to Mexico at Morelos Dam,
located 1.1 miles downstream from where the California-Baja
California land boundary intersects the river between the town of
Los Algodones in northwestern Mexico and Yuma County, Ariz.
The Colorado River Delta is located
at the natural terminus of the Colorado River at the Gulf of
California, just south of the U.S.-Mexico border. The desert
ecosystem was formed by silt flushed downstream from the Colorado
and fresh and brackish water mixing at the Gulf.
The Colorado River Delta once covered 9,650 square miles but has
shrunk to less than 1 percent of its original size due to
human-made water diversions.
This printed issue of Western Water examines how the various
stakeholders have begun working together to meet the planning
challenges for the Colorado River Basin, including agreements
with Mexico, increased use of conservation and water marketing,
and the goal of accomplishing binational environmental
restoration and water-sharing programs.
This printed issue of Western Water examines the
Colorado River Basin Water Supply and Demand Study and what its
finding might mean for the future of the lifeblood of the
Southwest.
This printed issue of Western Water explores some of the major
challenges facing Colorado River stakeholders: preparing for
climate change, forging U.S.-Mexico water supply solutions and
dealing with continued growth in the basins states. Much of the
content for this issue of Western Water came from the in-depth
panel discussions at the September 2009 Colorado River Symposium.
This printed copy of Western Water examines the Colorado River
Delta, its ecological significance and the lengths to which
international, state and local efforts are targeted and achieving
environmental restoration while recognizing the needs of the
entire river’s many users.
