Water pumps one possibility for unprecedented delta fish decline | TahoeDailyTribune.com
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Water pumps one possibility for unprecedented delta fish decline

Rich Pedroncelli / The Associated Press / A small fish was gathered from the fish screens leading to the federal pumps in Tracy in February.
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TRACY (AP) – Giant pumps in the Sacramento-San Joaquin River Delta are the heart of the state’s massive water system, sending water from it where it is most plentiful in Northern California to cities in the south and farm fields in the Central Valley.

Scientists are studying whether the pumps that are so essential to Californians’ everyday existence also may be one of the main culprits in an unprecedented die-off of fish species that are considered indicators of the delta’s environmental health.

“This is the lifeblood of billions of dollars worth of agriculture and urban water,” said Jeff McCracken, a spokesman for the U.S. Bureau of Reclamation, the agency that operates the federal system.



The state and federal pumps solve a fundamental water imbalance, where 70 percent of river water is north of Sacramento but 80 percent of demand is south of the capital.

But the pumps also lead to a variety of unintended consequences. They kill fish by sucking them in and alter the delta’s natural water flow. Researchers say even changes in the pumping schedule that were intended to benefit fish species may have backfired and are doing more harm than good.



Pumping during winter has increased about 30 percent since 2000. The goal behind changing the schedule was to leave more water in the delta during spring and summer, when spawning fish were thought to need it most.

Since then, however, scientists have documented a proportional increase in fish being killed through the pumps. Female fish that get sucked into the pumps during winter die before their eggs are fertilized, one possible reason for the perilous decline in delta smelt.

A similar pattern emerged during the early 1980s when wintertime pumping also was increased, although researchers have yet to prove a link to the decline in fish populations, said Ted Sommer, an environmental specialist with the state Department of Water Resources.

Smelt are driving much of the research into the delta’s decline because they are federally protected. Populations of striped bass, longfin smelt and threadfin shad also are falling.

Scientists fear the fish species’ decline is a harbinger of larger environmental problems in California’s vast delta, which provides water for more than two-thirds of the state’s residents. The largest estuary on the West Coast, it drains more than 40 percent of the state’s land mass and irrigates 4 million acres.

Pesticides, changing water chemistry and invasive foreign species all may be contributing to the decline of the fish populations.

Researchers also are increasingly examining the role the pumps and the pumping schedule may play.

Underscoring the complexity of the delta’s ecosystem, scientists outline the following scenario they say relates the pumps and environmental changes to the decline of the smelt: Water releases from upstream reservoirs slow significantly in late fall, allowing salt water from San Francisco Bay to intrude further into the delta. That provides a sort of highway for populations of an Asian clam that has infested much of the estuary.

Those clams reproduce quickly and compete with smelt, which average 3 inches in length, for food by filtering much of the delta of plankton. That forces smelt populations further upstream in their search for food and into the main pumping areas, where greater numbers of the fish are susceptible to getting sucked into the system.

One solution is to alter the flows from reservoirs so more water can be released in the fall, maintaining a healthier salinity balance that will keep the clams closer to the bay, said Christina Swanson, a scientist with the nonprofit Bay Institute.

“We don’t want to be in a position where we don’t do something because we’re not quite certain about it, and (then) we’re in worse shape next year,” she said.

A handful of studies, some funded by water districts that draw from the delta, show no definitive connection between the pumps and declining fish populations, said B.J. Miller, a consulting engineer with the San Luis and Delta-Mendota Water Authority, which represents 30 mostly rural water agencies. He says the problem is the clams.

Water users spend about $50 million a year buying from other sources to compensate for water that is left in the delta to aid the smelt.

Inside the federal pumphouse near Tracy, between Stockton and the eastern San Francisco Bay area, powerful motors drive six fan-shaped impellers that each pump half a million gallons of water a minute. The water flows through three tubes with enough power to lift it 200 feet over a mile, where it flows into the Delta-Mendota Canal for the trip south. State pumps nearby are even larger, pouring water into the California Aqueduct.

Most of the fish caught in the pumps die immediately or are sucked out later when farmers draw water from the canals for their fields.

Studies into the pumps’ impact are part of a larger, $3.7 million project targeted at finding the causes for the delta’s environmental decline. Among the angles and solutions scientists are examining:

– Are the pumps killing too many fish during winter? If so, the seasonal pumping schedule could be altered again.

– Is fall pumping leading to higher salinity levels in the delta? Reducing the amount of water pumped and releasing more water from reservoirs would send more fresh water into the delta, potentially giving the smelt a wider range.

– Can water be redirected through the delta to keep fish out of the pumps? The $110 million South Delta Improvement Project would install four retractable barriers to divert fresh water from the Sacramento River to the pumps, while helping keep fish away from the pumps. The retractable barriers would replace rock dams that are installed and removed each year.

“How can we get more water down to the pumps without jeopardizing the fish? That’s what we’re studying,” said Donald Kurosaka, a project manager with the state water agency. “If we can build structures that can direct fish out of the delta, that would be better than having to salvage these fish at the pumping facilities.”


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