We’ve heard the reasons for saving the Delta before: The salmon stopped running. Fish populations are crashing. The river is too salty.

Now, there’s a report that an annual survey found only 25 of the endangered Delta smelt, when the annual average found between 2000 and 2006 was 353.

General response: Boo freakin’ hoo.

When 25 million people and thousands of acres of farmland rely on Delta water, it’s hard to generate sympathy for the plight of the smelt, even though it appears they’re nearly extinct. Sure, fish gotta swim, but humans have to drink and eat.

So when talk turns to restoring water flow in the San Joaquin River and reducing pollution, it’s not surprising that the support is less than overwhelming. And when a judicial order forces the State Water Project to shut down its giant Tracy pumps because they suck up and kill endangered species, not many people raise a big stink when the pumps keep going.

Faced with the prospect of weakening the Central Valley’s agricultural behemoth and putting a crimp in water deliveries to Southern California, it’s no wonder environmental save-the-Delta concerns haven’t gained maximum traction.

But there’s another pretty good reason — aside from just being good stewards of the Earth — to restore the health of the Delta: Humans need a healthy Delta as much as the smelt.

It’s a peculiar thing about natural resources. Exploit them too much, and they become unexploitable. Fish so much that you destroy the stocks, and no more fish. Clear the farmland of native trees and grasses, and the fertile topsoil blows away. Suck so much water out of the Delta that you turn it into a salty, stagnant, polluted mess, and there’s no more water worth sending to farms and homes.

Here in the San Joaquin Valley, we’re about to tip that balance. Maybe we already have.

Humans have been altering the landscape since fire was discovered. Even “natural” societies like many Native American tribes cleared and burned brush and forest. But, for the most part, these groups were part of the balance of the ecosystem. If they overhunted or disrupted habitat or polluted their drinking water, they died. They had a huge incentive to not over-exploit their surroundings.

Since the advent of more urban societies — especially since the industrial revolution — we’ve had the capability (and tendency) to blow that balance.

Of course, the consequences for wildlife are staggering. Ask the Delta smelt, if you can find any. But the implications for people should be no less frightening.

When Anglo settlers killed off millions of bison that used to roam the Great Plains, the societies built upon that natural resource collapsed and ended up on “reservations,” a nice name for government detention centers. When fish stocks in the Grand Banks started to disappear, whole villages and towns vanished with them. When the mouth of the Mississippi River became so dammed and diverted that the bayous and sand banks shrank, New Orleans lost its natural protection from giant storms.

If our Delta becomes too crippled, the breadbasket of the nation might also end up on life support.

The disappearance of the smelt is a sign that we’re close. “The Delta smelt are an indicator species,” Dan Bacher told the San Francisco Chronicle on Tuesday. “If the smelt go extinct, other species are going to follow.”

As might our ability to rely on a healthy water source.

There’s going to be a hefty price tag attached to a Delta rebuilding project. And it’s going to be more than the $250 million Congress is ready to spend up front on restoration — including water rationing and impacts on the agricultural industry. Fixing the Delta, however, is worth it, for humans as well as fish.

The short-term costs of restoring the Delta are indeed high. But not doing anything will someday cost us much, much more.

To contact Jon Mendelson about his weekly column, e-mail jmendelson@tracypress.com.