The slender Delta smelt grows to about three inches, lives for less than a year and is a poor swimmer.
With its diminutive size and the Delta's murky waters, it's often hard to see.
But the threatened smelt holds a very visible and important spot in California's water wars and perhaps an even bigger place in the massive estuary to Lodi's west.
The smelt took center stage last month when its sharp decline forced officials to temporarily shut down the state's water pumps near Tracy - pumps that channel water to 25 million people, mostly in the Bay Area and Southern California.
Environmentalists say the move was necessary to save not just the smelt but perhaps scores of other declining species in the Delta.
"It's a sentinel - the proverbial miner's canary … an indicator of the overall health of the estuary," said Bill
Jennings, a staunch environmentalist and executive director of the California Sportfishing Protection Alliance. "When you start breaking links out of the (food) chain, there are ripple effects up and down it."
The state water pumps - blamed for sucking many of the small fish from the Delta's waters to their deaths - were turned back on earlier this month, though at a lower flow.
Fish such as the splittail and threadfin shad, striped bass and salmon are all on the decline and could perish if the smelt disappear, Jennings said.
State and federal agencies list the species as threatened, though many environmentalists consider the smelt on the brink of extinction.
The best estimates say there were more than a million smelt at the species height and as few as 35,000 today, said Tina Swanson, a senior scientist for the nonprofit Bay Institute, who's spent much of her career studying the fish.
Females produce between 1,000 and 2,600 eggs. Larvae hatch between 10 and 14 days. Most smelt die after spawning in the early spring, though a few survive to a second year. Smelt feed entirely on small crustaceans called zooplankton, a species that has also declined in the Delta.
Source: California Department of Fish and Game.
Dramatic population declines in the 1980s led to federal and state protection for the smelt in 1993.
Historically, the smelt were among the most abundant fish in the Delta. They served primarily as food for larger fish, though a few, mostly Asian fisheries, targeted the species and the larger longfin smelt in the early 1900s.
The fish are spawned in the freshwater of the Delta during the early spring. As young fish, they then migrate to the brackish water of San Pablo Bay by early summer before returning late in the year to lay their eggs back in the Delta.
The smelt are not always easy to see, but they do have a unique smell.
"They smell like cucumbers when you get them on your hand," said Dan Odenweller, a retired senior fishery biologist who worked for more than 30 years for the state Department of Fish and Game.
The decline in the number of smelt has continued, and even accelerated, in recent years.
"The fish is closest to extinction as any fish that exists in this system," Swanson said, noting that spring surveys showed the number of young smelt declined by 90 percent from last year.
"If this pattern holds, our fear is there is going to be very few adults," she added. "It a real worry that it's going to be very hard to recover this fish."
Demands for water continue to grow throughout California as the number of smelt shrink. Odenweller said the state is now in a difficult position, deciding whether to slake the thirst of its residents or protect its native species.
"That is the dilemma of water management in California," he said.