Important planning efforts are under way that will impact two-thirds of California residents, including residents of the Bay Area. Many people are unaware of them, and even for those who are, it's pretty confusing because water issues in California have always been complicated.

Simply put, two-thirds of the water supply in California comes from rainfall in the northern part of the state, and more than two-thirds of the population lives in the southern part of the state.

Most of that water flows into the Sacramento and San Joaquin rivers, through the Delta into San Francisco Bay and to the Pacific Ocean.

Over the years, Californians have devised an intricate plumbing system to divert water for various human uses in the north and south of our state; parts of that plumbing don't work very well for our 21st century world.

The two plans to reallocate that water more equitably are quite different, yet have similar names: the Bay Delta Conservation Plan (BDCP), and the Bay-Delta Water Quality Control Plan.

BDCP is a plan for new conveyance facilities and habitat restoration. The Bay-Delta Water Quality Control Plan updates regulatory requirements for flows allocated to human and nonhuman uses.

These two plans and the final decisions that will be made by the State Water Board will greatly impact the future of the San Francisco Bay and Delta by determining how much fresh water from the Sacramento and San Joaquin rivers will flow through the Delta and into the Bay.

When you see the San Francisco Bay, the strait from the Carquinez Bridge, or the Delta, you see a lot of water so it's difficult to grasp that they have been in a state of chronic drought for the past decade and more.

The ecosystem of the Bay-Delta depends on a dynamic balance between salt water from the ocean and fresh water from the creeks and rivers that supply it. This balance shifts throughout the year with rainfall and tides, creating a unique and changing system that historically sustained legendary salmon runs, shellfish beds, tremendous shorebird migrations, and other natural riches.

Over the past several decades, ever larger quantities of fresh water have been diverted from this system for human use, captured in dams and reservoirs and diverted by pumps, canals and pipes before reaching the Bay.

The balance between salt and fresh water has been lost, with devastating impacts to the ecosystem and certain segments of our economy. According to The Bay Institute's report "Gone with the Flow," "annual freshwater inflows into the Bay have been reduced by more than 50 percent with increasing frequency in the last several decades. In 2009, barely a third of the watershed's total runoff reached the Bay."

Despite millions of dollars invested to clean up the Bay-Delta and restore habitat, none of our fish communities have improved in the past 20 years. Six native fish species have been listed as endangered under federal and/or state guidelines.

Scientific studies show that fish species are declining rapidly, including commercially important and endangered salmon, sturgeon, smelt and several species of sport fish.

Why do we need a healthy estuary? It's about more than endangered Delta smelt, which receives enormous attention for its diminutive size. It's about salmon, sturgeon, herring and Dungeness crab, the people who eat them, and whose lives depend on their harvest.

It's about water quality in the Bay and Delta, which needs fresh water from winter storms to flush pollutants out of the system. It's about the impacts that degraded water quality will have on all residents of this area, not just those who receive their drinking water from the Delta.

In 2012, the Contra Costa County Board of Supervisors passed a resolution recognizing the Bay and Delta as critical to the health of our regional economy and to ensure protection and restoration of a healthy sustainable ecosystem, including adequate water quality, flows, and water supply to support fisheries and wildlife.

The resolution also called for protection of the economic viability and vitality of communities throughout the Delta and along the shoreline of the greater San Francisco Bay-Delta. Similar resolutions were passed by the cities of Brentwood, Clayton, Danville, Martinez, Pinole, San Ramon and Walnut Creek, and by the Association of Bay Area Governments (ABAG) representing the nine-county Bay Area and 7 million residents.

The BDCP and the Bay-Delta Water Quality Control Plan will determine the future of the San Francisco Bay and Delta ecosystem and whether it continues to decline due to excessive diversion in canals or pipelines, or whether it can be restored to health.

Both plans have pros and cons for the Bay Area -- neither is a panacea for the health of our Delta and Bay.

Hopefully, the Bay Delta Conservation Plan and the Bay-Delta Water Quality Plan will reflect the priorities of our residents, and the State Water Board will develop plans that ensure adequate freshwater flows through the Delta and San Francisco Bay.

Those decisions on methods of deliverance and quantities of diversion will dramatically impact the quality of our environment and the vitality of our region for generations to come. Stay tuned for more information as the process continues.

Pierce is the mayor of Clayton. Email her at columns@bayareanewsgroup.com.