As we sailed beneath the mile-long motorway bridge, our boatman pointed up and said in Portuguese, ‘Golden swallows’.
I have never seen such a sight.
There were thousands of them. They were swirling around like flies.
Their mud nests plastered the milk-white span of concrete. At last an ecologically-friendly motorway, I thought.
We reckoned perhaps 2,000 nests at least were attached beneath this bridge of biodiversity.
The birds are known to us as red-rumped swallows. They are like our swallows, but also our house martins, a sort of cross between the two.
If you see pictures of them in books you can see why they are golden to the Portuguese. We were on the second largest reservoir in Europe at Monsaraz in the Alentejo district, which is north of the more popular Algarve.
Not so many tourists, but hot, hot, hot. Lovely. We landed on a tiny island. ‘Golden Island’, declared the boatman.
It was true. Another name could be Treasure Island. Wavelets lapping the sand
had isolated a dense littoral of gold specks, known as fool’s gold, which gleamed brilliantly in the sun.
We swam to another island nearby, my grand-daughter Beatrice, now a ballerina in the State Company, leading the way.
When the Guadiana River was dammed 12 years ago, a whole village and many farms were inundated by 250 square kilometres of water, leaving islands and a shoreline longer than the whole of the Portuguese sea coast.
Old olive trees still grow on the islands, and the rabbits which were marooned now live safely from predators, but on a much reduced Ben Gunn diet.
One segment of this vast inland sea reminded me of the view of Chichester Harbour and the Solent as seen from the top of Kingley Vale.
Driving on south to Moura, my grandchildren, son, wife and daughter-in-law all waited patiently while I scanned the muddy margins of the reservoir as flocks of water birds suddenly came in to view.
Gadwall, pintail, teal were all dibbling happily where once the goat and gheko roamed. White storks and purple herons sat hunched and well-fed on the tops of stone walls that once had been field boundaries.
Black-winged stilts and redshanks picked through the mud that once grew sweetcorn or barley.
Here was another Medmerry as we have recently seen in Sussex at Bracklesham.
Apart from the difference in size, this lake in the Alentejo will provide fresh water for the region even if there is a total drought that lasts three years.
When we first saw this region 20 years ago, the living was tough with small-holders eking a living with donkeys and an old olive tree or two, the hills as brown and dry as desert.
Now 100,000 hectares have been turned dark green with new olive plantations, each tree given water down its own little pipe.
There’s now gold in those hills, and even the swallows have turned to gold.