Two men, out on a boat for an afternoon’s fishing, simply disappeared from sight and are feared drowned.
Another man, fishing from a boat in the same part of the Alqueva reservoir in the São Marcos do Campo area, said that one minute they were there and the next, they were gone.
Members of the local GNR and local firefighters searched as best they could in the deep water and fading light but, as at the end of Sunday, had found nothing.
A source from the GNR said that the warning was given at 16:35 by a man on a boat who was fishing on the vast expanse of water, but that the two men disappeared from view.
The missing men are described as being between 45 and 50-years-old.
A fishing boat later was found near the bank of the reservoir and indentified as belonging to the missing men.
Boats and specialist divers soon were at the scene and will recommence the search on Monday morning.