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.
The San Diego County Board of Supervisors unlocked
approximately $6 million in reserves and is planning to spend a
portion of that money on evaluating the first phase of a
project to build a new treatment plant, separate from the
existing South Bay plant, to capture and treat Tijuana River
sewage flows. On Sept. 1, the board established the Tijuana
River Capture and Cleanup Initiative with three phases to build
a new treatment plant near the U.S.-Mexico border, at a
starting cost of $1.8 million to evaluate options including
past proposals. A county board letter about the initiative
does not include a total price estimate nor where that money
would come from or the treatment capacity for the plant and
where it would be built. However, the letter says the first
phase will consider a 2021 river diversion study by the U.S.
Environmental Protection Agency.
The San Diego County Board of Supervisors voted Tuesday to
launch a new phase of the county’s fight against Tijuana River
pollution, approving funding to plan a new treatment
system to capture sewage from the river itself and to
advance a permanent fix at a toxic air pollution hot spot in
South County. … The capture and cleanup measure directs the
county’s chief administrative officer to begin an 18-month
project development and engineering analysis, funded by $1.8
million from the county’s Unlocked Reserves Framework,
according to a county staff report. … A separate measure
allocates $4 million to advance design, environmental review
and permitting for a permanent box culvert
project at Saturn Boulevard, where hydrogen sulfide
levels have reached 16 times the state air quality
standard.
After decades of pollution and years of beach closures caused
by raw sewage in the Tijuana River, San Diego County
Supervisors are pursuing a local plan to divert the
river and treat it directly. They’re calling for the
county to design a new treatment plant to capture and
clean contaminated water before it enters San Diego
communities, using potential local tax revenue to back
nearly a billion dollars worth of bonds to build it.
… The supervisors called for spending $1.8 million to
design a system to divert and treat the river water. They also
proposed $4 million to immediately fix a sewage hot spot on
Saturn Boulevard, where river pollution becomes aerosolized.
The board will vote on the plan Tuesday.
… On Monday, board chair supervisor Tara Lawson Remer and
Supervisor Paloma Aguirre will unveil a new proposal.
… The idea is to design a treatment system on the U.S.
side of the border that catches the raw sewage before it moves
down stream in San Diego communities and beaches. It appears
the construction of this type of infrastructure would happen in
phases. While the details of the proposal are still up in the
air, Board Chair Supervisor Tara Lawson Remer and Supervisor
Paloma Aguirre will unveil some of the specifics at a press
conference Monday. … County Supervisors said they hope
introducing this new initiative will protect the public health,
environment, and local economy; and get the Tijuana River off
the American Rivers conservation group’s most endangered list.
Members of the United States Section of the International
Boundary and Water Commission, Environmental Protection Agency
and state officials gathered during a New River roundtable on
Tuesday, Aug. 18. Updates were provided on the status of New
River improvements on both sides of the border, including
agency collaboration and a water sampling study. The New River
is located 20 miles south of Mexicali and flows north. After
crossing the border, it travels 65 river miles northward
through Calexico and the Imperial Valley before emptying into
the Salton Sea. … According to the presentation, the EPA
has invested roughly $44 million across seven Mexicali
infrastructure projects.
Federal, state, and local leaders gathered in Calexico to
inspect the ongoing environmental and public health crisis
plaguing the New River, signaling a renewed, coordinated
push for a permanent solution to decades of
transboundary pollution. … For decades, toxic waste
has flowed north across the U.S.-Mexico border through the New
River. The pollution causes significant ecological and health
damage to Calexico residents and local communities stretching
all the way to the Salton Sea. Now, the City of Calexico’s “New
River Project” functions as a temporary defense system
by screening heavy trash out of the water as it crosses the
international border.
Federal environmental agencies and local leaders will gather in
Calexico later this month to update the public on ongoing
efforts to address long-standing pollution in the New River, a
vital cross-border waterway flowing from Mexicali, Mexico, into
California’s Imperial Valley. The U.S. Section of the
International Boundary and Water Commission (USIBWC) and the
U.S. Environmental Protection Agency (EPA) announced they will
co-host a hybrid public roundtable on Tuesday, Aug. 18, from 11
a.m. to 1 p.m. PDT. … For decades, the New River has
carried industrial wastewater, agricultural runoff, and
untreated sewage northward across the U.S.–Mexico border,
creating persistent public health hazards and environmental
concerns for residents in Calexico and surrounding Imperial
County communities.
A long-running binational effort to improve wastewater
infrastructure in the Tijuana-San Diego region has reached a
new milestone, with authorities reporting significant progress
on projects designed to reduce cross-border sewage pollution
and improve water treatment. According to Baja California’s
Secretariat for Water Management, Sanitation and Protection
(SEPROA), the initiative represents a joint investment of more
than 15.6 billion pesos (around $900,000) by Mexico and the
United States. SEPROA Secretary Víctor Daniel Amador
Barragán said authorities are overseeing 20 infrastructure
projects grouped under 16 initiatives established through
Minute 328, a binational agreement focused on modernizing
wastewater infrastructure in the Tijuana River watershed.
The Trump administration has ordered construction crews on a
border wall to stop drilling wells in drought-stricken New
Mexico after ranchers saidpumping
groundwater needed to make concrete could threaten their
livestock. The order comes as crews across the
southern border race to complete one of President Donald
Trump’s highest domestic priorities — barriers that span four
states and received over $46 billion in federal funding.
Controversies have sprouted up in Texas and
California, with border-town residents and
environmentalists reporting a wide variety of issues with
construction. U.S. Customs and Border Protection, which
oversees border wall construction, has said water is
needed to make concrete for roads, wall construction and dust
suppression. Cattle ranchers in the area say
the drought has already forced them to reduce their
herd size.
The U.S. and Mexico reached an agreement in June 2025 to work
together on a permanent solution for the sewage crisis in the
Tijuana River Valley. This comes after decades of the crisis,
leading to widespread pollution that closed beaches and filled
the air with toxic hydrogen sulfide. The original memorandum of
understanding outlined goals for both American and Mexican
construction of wastewater infrastructure: Minute 328. This
includes the expansion of the South Bay International
Wastewater Treatment Plant to 50 million gallons per day by the
end of 2027. “Mexico is on schedule with their commitments
that are made in those minutes,” said Mike Martucci, the
Administrator for EPA Region 9, which includes
California. Among those commitments are rehabilitating
pump stations and interceptors along the Tijuana River in 2026
and upgrading their wastewater treatment plants on the Mexican
side of the border in 2027.
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.
