STOCKTON (CBS/AP) — State officials say they are struggling to keep portions of the Sacramento-San Joaquin River Delta fresh as saltier water from the San Francisco Bay pushes inland during another summer of drought.

Normally, rivers push back saltier water and keep the delta fresh. But because of the drought, the rivers are low and bay water is invading parts of the estuary.

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According to the U.S. Geological Survey, about 25% of the Delta’s outflow is pumped in to California’s water system. Saltwater intrusion can ruin the water for agriculture and domestic purposes.

The state Department of Water Resources and U.S. Bureau of Reclamation earlier this year asked regulators to temporarily weaken certain salinity standards in the west Delta to hold back more bay water. The request was granted.

But officials say even those weakened standards have been exceeded in two locations — one on the Sacramento River at Three Mile Slough and another on the San Joaquin River at Jersey Point.

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“We knew things were going to be tight,” John Lehigh, who oversees operations of California’s water delivery system, told the State Water Resources Control Board this week.

Little water can be released from reservoirs to push back the saltier water, he said.

Some environmentalists have challenged the water board’s decision to allow those scientifically determined water-quality standards to be weakened. In a complaint filed Wednesday, the Stockton-based California Sportfishing Protection Alliance warned that the looser standards also imperil fish that already are on the verge of extinction, such as the tiny Delta smelt.

Stockton’s Restore the Delta filed its own protest on Thursday. “The system is really in quite a crisis,” said Tim Stroshane, the group’s policy adviser.

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