SAN JOSE — On a recent afternoon at Guadalupe River Park in the heart of downtown, a couple strolled hand-in-hand, a mother pushed her toddler in a stroller, and soft breezes rustled the leaves of stately trees near the home of the San Jose Sharks.

But something was missing: the river.

The river that runs through America’s 10th-largest city has dried up, shriveling a source of civic pride that had welcomed back trout, salmon, beavers and other wildlife after years of restoration efforts. Over the past two months, large sections of the Guadalupe have become miles of cracked, arid gray riverbed. Fish and other wildlife are either missing or dead, casualties of California’s relentless drought.

“I’m heartbroken,” said Leslee Hamilton, executive director of the Guadalupe River Park Conservancy, a nonprofit that runs educational and community programs along the river.

“We’ve been seeing a great increase in the number of birds and wildlife in the area,” she said. “The timing of this is just devastating.”

The Guadalupe is in worse shape than many California waterways, but it is hardly alone.

The state’s rivers and creeks are withering and in some cases disappearing entirely after four years of historically dry weather — the focus of the latest installment of this newspaper’s series, “A State of Drought.”

In the agriculture-rich Central Valley, the drought has slowed plans to release more water to the San Joaquin River to bring the over-tapped waterway back to life. Up north in Humboldt County, salmon are at risk of going high and dry in the tributaries of the Eel River.

“It’s grim,” said Matt Clifford, an attorney with Trout Unlimited, a nonprofit that has its California headquarters in Emeryville. “This is not good for wildlife or fish.”

Across the state, environmentalists are battling state, federal and local water agencies, arguing that more water should be released from reservoirs to save species in danger of extinction. In many cases, farmers and cities are clamoring for the same water, arguing that people must come first in an emergency.

“At the end of the day, there just is not enough water to maintain sufficient releases,” said Michelle Leicester, an environmental scientist with the state Department of Fish and Wildlife.

Nobody has an exact count of how many streams have run dry. Although some California rivers have gauges, they’re used mostly to monitor floods, not low water levels. And many remote creeks and tributaries that are vital to fish have no gauges installed by state or federal agencies at all.

“Every stream is slowly going dry. But it’s tough to give names and numbers,” said Gordon Becker, a fisheries scientist with the Center for Ecosystem Management and Restoration, a nonprofit in Oakland. “The system is hopelessly inadequate.”

Anecdotally, gold panners have reported sections of the Cosumnes and Bear rivers going so low in the Sierra foothills that they are finding long-hidden flecks of gold in the sediment. A month ago, state water officials ordered property owners in Sonoma County to reduce water use to stop four creeks from running dry that feed the Russian River, a critical home to endangered coho salmon.

“The deeper you get into the drought, the worse it gets,” Clifford said.

The Guadalupe River isn’t a big river or a storied river. But it has a long history in the area.

It was named in 1776 by Spanish explorer Juan Bautista de Anza for the Virgin of Guadalupe as he camped along its banks en route from Monterey to San Francisco.

The river starts in the eastern foothills of the Santa Cruz Mountains in smaller creeks. Those tributaries merge to become a river just south of Highway 85 in the Almaden area of San Jose. In normal years, it flows north through neighborhoods and downtown, then alongside Mineta San Jose International Airport before emptying into San Francisco Bay at Alviso.

Long neglected, polluted and lined with warehouses, the river began a renaissance in 2005 when San Jose, the Army Corps of Engineers and the Santa Clara Valley Water District completed a $350 million flood control project through downtown. The project also created the 250-acre Guadalupe River Park and Gardens.

Over the past decade, despite problems with homeless encampments, the river has become increasingly popular with bicyclists who use its growing trail network as well as community groups who have watched its fish and wildlife rebound.

Although parts of the Guadalupe have gone dry in past years, this year is far worse than anyone can remember.

The past four years have been the driest four-year period since 1850, when California became a state. Water releases from the four reservoirs located upstream on the Guadalupe and its tributaries — Lexington, Calero, Guadalupe and Almaden reservoirs — have been cut roughly in half this year by the Santa Clara Valley Water District, which owns them.

“We have to make some tough decisions,” said Aaron Baker, the district’s raw-water operations unit manager. “We are trying to best manage the water that we have. We are trying to make sure that we have drinking water for public health and safety across the county.”

Although state law requires dam operators in California to release water for fish, the National Oceanic and Atmospheric Administration and the state Department of Fish and Wildlife allowed the water district to reduce releases from the reservoirs from May through November.

Santa Clara Valley Water District officials made the case that with low storage in the county’s 10 reservoirs — now 46 percent full — even if a lot of water was released down the Guadalupe River, most of it simply would soak into the bone-dry soil. And within a month the river would be dry again.

Because less water is being released from the reservoirs, at least eight miles of the 14-mile Guadalupe River are now completely dry. And 12 of the roughly 30 primary miles of nearby Coyote Creek have suffered a similar fate.

So what happened to the fish and wildlife?

Nobody knows for sure. Indeed, no federal, state or local agency takes a regular count of the fish.

Only three chinook salmon were found last year returning from San Francisco Bay to spawn in the Guadalupe. And steelhead trout, an endangered species that in recent years has been seen in the river, are believed to have been wiped out for now.

Several beavers that were discovered two years ago in downtown San Jose along the river, delighting the public, appear to have moved miles away.

One was spotted several weeks ago on Los Gatos Creek in Campbell, said Steve Holmes of the South Bay Clean Creeks Coalition. That creek still has some water in it because the water district has been releasing 12 cubic feet per second from Lexington Reservoir, diverting three-quarters of it into percolation ponds to recharge groundwater.

The other 3 cubic feet per second is flowing downstream. But that’s not much, and the creek dries out before it meets the Guadalupe in downtown San Jose.

The lack of water does have a few positive effects, Holmes said. First, invasive species such as carp are dying off, so native fish left in the higher reaches of the river may be able to rebound better when the drought ends. Second, dry riverbeds are easier to clean, and Holmes’ group has removed 100 tons of trash over the past two years from Los Gatos Creek and the Guadalupe River — some of it in places that normally would be underwater.

As with other creeks that feed the Guadalupe River, including Guadalupe and Alamitos, minor releases from the water district’s reservoirs are keeping the higher reaches wet, preserving some wildlife.

All along the Guadalupe are signs of wildlife calamity, however: dead fish carcasses, dried trash, a few stagnant pools by the Children’s Discovery Museum.

“It is really sad. I’ve been watching the water go completely dry,” said Roger Castillo, an amateur naturalist who famously discovered the bones of a 20,000-year-old mammoth along the Guadalupe in 2005. “We’ve had massive fish kills.”

Still, Castillo said he’s seen some fish alive in storm drain pipes recently. And he’s hopeful that winter rains will bring the river back to life. Until then, he and other river lovers, including amateur naturalist Greg Kerekez, of Los Gatos, want the water district to rescue fish stranded in isolated pools and to train volunteers to better monitor what’s happening.

But water district biologist Jae Abel says relocating fish from drying parts of streams to wetter areas upstream could spread disease and stress the fish in the healthier areas.

“The best we can do is hang on to some of the stream,” he said, “even if we can’t save the rest.”

Paul Rogers covers resources and environmental issues. Contact him at 408-920-5045. Follow him at Twitter.com/PaulRogersSJMN.