他把七十英亩麦地还给了水：现在那里住着一百四十种鸟，和两种快没有了的鱼

Let's start with a sentence, said by a farmer.

He said: this place always wanted to be a wetland.

It sounds a little literary, but what it describes is something very concrete.

The setting is southern Oregon, beside a lake called Upper Klamath.

By the lake there is a farm, four hundred acres, growing barley for close to a hundred years.

Three generations, all of them farming it.

The trouble comes in winter.

This is low ground, and every winter the fields flood.

When the water drains back into the lake in spring, the problem arrives.

The water carries phosphorus out of the fields and into the lake.

Phosphorus comes from fertiliser; it is good for crops, and not good for a lake.

Once there is too much phosphorus in a lake, the algae bloom.

Once there is too much algae, the oxygen in the water drops.

And the fish are the first to suffer.

There are two kinds of fish in this lake, called the shortnose sucker and the Lost River sucker.

They live only in this one water system, nowhere else.

Both are now endangered species protected under United States federal law.

Their problem has an unusual shape: the adult fish are still alive, and the young ones almost never reach adulthood.

With water quality this poor, the juveniles do not survive their first year.

The farmer thought about it for many years.

Then he made a decision that looked very strange to his neighbours.

Out of four hundred acres, he took seventy out and stopped planting them.

He put water back onto those seventy acres and built a managed wetland.

Note that he did not sell the land, and he did not leave farming.

On the remaining three hundred and something acres, he still grows barley.

What this wetland does is essentially work as a filter.

The water slows down inside it, the phosphorus settles to the bottom, and the water plants take it up.

The water that then flows into the lake is far cleaner.

One piece of land went from being the source of the problem to being the thing that treats it.

The change came faster than expected.

First the grass grew, then the insects came, then the birds.

Today, a hundred and forty bird species have been recorded on those seventy acres.

In winter, tens of thousands of ducks, geese and swans stop there.

Otters live in the water too, along with beavers and muskrats.

But the fish are what matter most.

Researchers put those two endangered species into the wetland to rear them.

The water is shallow, food is plentiful and predators are few — exactly right for young fish.

Last year they lowered the water level in part of it and counted what had survived.

They came out with fifty fish that had reached adult size.

Fifty does not sound like many, but for two species whose juveniles do not survive at all, it is a real signal.

This is worth telling because it is more a re-doing of the arithmetic than a story of conservation against farming.

A patch of low ground that flooded every year and was hard to farm turned out to be worth more used another way.

The lake water got cleaner, and the remaining land became easier to farm.

The farmer stayed where he was, the birds came back, and the fish survived.

Think about it: is there a place near you that everyone keeps forcing into one use, when it would suit another far better?