LOS ANGELES — Powerful pumps that supply much of California’s population with water have killed several thousand threatened and endangered fish this year, prompting a coalition of environmental groups to demand that state and federal agencies take immediate steps to limit “alarming levels” of deaths.

In a letter to state and federal water managers, leaders of five fishing and environmental groups said the estimated losses of threatened steelhead trout and endangered winter-run Chinook salmon have exceeded maximum annual limits for water intakes in the Sacramento-San Joaquin River Delta.

“Given that these and other species in the Bay-Delta are at grave risk of extinction, we want to emphasize the need for urgent action,” the environmental advocates wrote.

The massive pumps that draw water into the aqueducts of the State Water Project and the Central Valley Project are strong enough to reverse the flow in parts of the south delta. They can also suck fish into their machinery or make them easy prey for predators. Because of this, pumping facilities are assigned annual take limits for certain fish under the Endangered Species Act.

The environmental groups are urging water managers to scale back pumping until juvenile salmon and steelhead have finished migrating through the delta and into San Francisco Bay.

“To see the state and federal water agencies exceed their take limits and continue business-as-usual water exports is like witnessing extinction in real time,” said Jon Rosenfield, science director of San Francisco Baykeeper. “It demonstrates the official negligence and lawlessness that caused these fish, and many others, to become endangered in the first place.”

State water officials say they have been taking substantial measures to protect fish. They say the large numbers of fish that have moved into areas around the water intakes have caused them to pump less than they typically would based on current conditions.

The losses are calculated based on the numbers of fish that are collected — scooped from the water in a bucket-like device at the state facility — then transported by truck and released into the delta nearby. The calculations attempt to account for fish that are caught by predators and those that are killed when they are drawn into pumps.

According to the California Department of Fish and Wildlife, estimated losses of steelhead trout exceeded the annual incidental take limit of 2,760 on March 20. By the end of March, the department said, the estimated losses of naturally spawned steelhead since Dec. 1 had risen to 3,374.

The estimated losses of endangered winter-run Chinook salmon also exceeded the annual loss threshold of 2,748 on March 20. Those estimated losses have since risen to 4,049, according to the Department of Fish and Wildlife.

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