Gov. Arnold Schwarzenegger has proposed $4.5 billion in bonds to build two new dams, which his administration says are needed to boost water supplies. Most Democratic lawmakers and conservationists are opposed. Here are some of the issues involved in the debate:

Q: Why are more dams under consideration?

A: Scientists say climate change will reduce California's snowpack - its largest source of water - by as much as 90 percent by the end of the century. Department of Water Resources director Lester Snow has said dams are a key part of the state's strategy to accommodate future population growth and the effects of global warming.

Building more reservoirs would give the state more space to store about 3 million acre feet of water. By comparison, Lake Oroville north of Sacramento holds about 3.5 million acre fee. The additional water likely would be used for water supply, restoration of fish habitat and improving water quality.

The additional dams also could provide more places to send water when rivers in Northern California and the Central Valley are close to topping their banks and levees, potentially saving communities below the dams from flooding.

Q: What are some of the concerns about building new dams?

A: Dams are expensive and alter the natural flows and habitats of rivers. Opponents say a dwindling snowpack could make some existing dams obsolete because global warming could lead to less water flowing from the Sierra as snowmelt. They say the state should invest money on alternatives such as conservation efforts, desalination, water recycling and recharging groundwater.

Q: Where could dams be built?

A: The state has two leading candidates for new reservoirs. The first is known as Temperance Flat in the narrow canyon above Millerton Lake on the San Joaquin River, northeast of Fresno. It could hold up to 1.3 million acre feet of water, which local officials and farmers say they need to satisfy agriculture and a growing population.

The state is considering another area along the Sacramento River in the rolling hills and grasslands of the Antelope Valley, about 60 miles north of the state capital. River water would be diverted to the valley and would flood about 14,000 acres.

Q: Why don't we just finish the Auburn Dam?

A: It's the project that never seems to go away. Congress approved a dam along the American River in the 1960s as a way to provide more water to farmers in the Sacramento and San Joaquin valleys. But a 5.7-magnitude earthquake in 1975 north of Sacramento exposed a fault line that ran under the construction site, bringing the project to a halt.

Republicans in Congress are anxious to get construction crews back to the dam site in the Sierra foothills east of Sacramento. Supporters say it will improve Sacramento's flood protection, but recent cost estimates have put the price tag at more than $10 billion. It's unlikely the Democrat-controlled Congress will back such an expensive dam in a scenic canyon of the American River.

Q: What are the alternatives to dams?

A: Local water agencies are trying to improve methods to recycle water for use at industrial plants, to recharge groundwater basins and restore habitat. Some coastal cities are considering removing salt from sea water, but the technology is expensive.

Pumping water into the ground could free up reservoir space, but one limitation is the amount of time it takes for water to seep into deep aquifers.

The state Department of Water Resources estimates that cities can save up to 2.3 million acre feet of water by encouraging residents to install low-flush toilets and other water-efficient devices. Meanwhile, farmers can reduce the amount of water used for agriculture by as much as 2 million acre feet by 2030 if they use water-saving pipes and switch to crops that require less water.

Q: Is the Peripheral Canal back?

A: State Sen. Joe Simitian, D-Palo Alto, has introduced a bill that would allow for a canal that sends Sacramento River water around the delta. The idea was resoundingly defeated by voters in the 1980s, but the fragility of the Sacramento-San Joaquin Delta has led some researchers to give the proposal another look.

A canal would deliver fresh water directly to the San Francisco Bay area and Southern California. Relying on the delta is risky for several reasons: Rising sea levels or a break in an earthen levee could contaminate delta water with higher levels of salinity, making it useless for municipal and agricultural use.