The Delta Conveyance Project — often called the Delta Tunnel — remains one of California’s most hotly debated infrastructure proposals. Though not yet under construction, it looms large in political, environmental, and water-management discussions as state leaders grapple with how to secure water for millions of residents and withstand future climate challenges.  

What the Project Is

The Delta Conveyance Project proposes building a 45-mile underground tunnel under the Sacramento-San Joaquin River Delta — California’s largest estuary — to move water more reliably from the wetter northern region to the south and statewide water delivery systems. The idea is to shield the State Water Project from earthquake vulnerabilities and capture more water from storms and rainy periods.

If built, the new tunnel structure would ultimately help ensure water deliveries to about 27 million Californians and roughly 750,000 acres of farmland.

Huge Cost, Slow Progress

The project’s price tag has soared over time. The latest state estimates place **construction costs at roughly $20 billion (up from earlier estimates), with water agencies and districts in several regions voting to spend tens of millions on additional planning and permitting.  

Critically, there is still no active tunnelling — the project remains in planning, permitting, and political debate phases. Final decisions on major funding, environmental reviews, and approvals will determine whether and when it moves forward in earnest.

Political and Legislative Battles

The Delta Tunnel has become a flashpoint in Sacramento:

• Gov. Gavin Newsom has repeatedly pushed to “fast-track” the project as part of state budget plans and water resilience strategies, arguing that streamlining permitting and approvals will protect California from future droughts and climate extremes. He also announced a $200 million accountability and community benefits plan aimed at supporting Delta communities during construction.
• A broad and growing coalition of legislators — particularly members of the California Legislative Delta Caucus — has consistently opposed fast-tracking plans, calling the tunnel unaffordable, destructive, and unnecessary. This group has pushed back against budget proposals that would bypass environmental and judicial oversight and has urged greater study of alternatives like water recycling, groundwater storage, and levee fortification.
• In mid-2025, the California Senate budget committee rejected a trailer bill package tied to the tunnel’s budget and funding mechanisms, signalling that the Legislature may resist attempts to rush the project ahead.

This legislative push-and-pull reflects deeper policy debates about priorities in water infrastructure and how best to meet the state’s long-term needs.

Environmental Concerns Remain Central

Environmental advocates continue to highlight significant ecological risks associated with the project:

• The Delta ecosystem is already stressed; species like the Delta smelt and salmon have seen dramatic declines. Opponents argue the tunnel could worsen habitat loss, reduce freshwater flow through natural Delta channels, increase saltwater intrusion, and drive toxic algal blooms.  
• Tribes, environmental justice groups, and Delta farmers have rallied against the tunnel, warning that decades-long construction and altered water flows could damage cultural resources, native habitats, and local livelihoods.  

Environmental debates are tightly interwoven with political ones; critics of fast-tracking cite environmental review protections as guardrails that must not be weakened for expediency.

Economic and Community Impacts

Supporters of the Delta Tunnel argue that without major new infrastructure, California risks more severe water shortages, especially as climate change drives hotter, drier conditions punctuated by intense storms. A state report framed the tunnel as a key strategy for maintaining reliable water deliveries to millions of people.  

Yet opponents counter that investments like recycling water, capturing stormwater, and bolstering local storage may be cheaper and less disruptive than the $20-plus billion tunnel. They also warn that the tunnel’s construction could disrupt Delta ways of life for years and burden ratepayers with increased utility costs

What Happens Next

As of late 2025:

• Construction has not yet begun, and major decisions about funding mechanisms, environmental reviews, and legislative approval remain unresolved.  
• The governor and water agencies continue to advocate for the project, emphasizing earthquake resilience, climate resilience, and long-term water reliability.
• Lawmakers and local communities are pressing for deeper scrutiny of environmental impacts and more sustainable alternatives, and budget committees have pushed back on fast-tracking mechanisms that could curtail oversight.  

In this sense, the Delta Tunnel embodies the broader California water dilemma — balancing urgent infrastructure needs against environmental stewardship, fiscal responsibility, and community concerns.