The operative group that included agents from the Spanish Civil Guard's Nature Protection Service (Seprona), the Group Specialised in Underwater Activities (GEAS) and specialised biologists from the Chelonia association decided to finish the work after six days of unsuccessful searches.

On Saturday, 6 June, the Spanish Civil Guard learned of a possible sighting of a Nile crocodile, weighing around 250 kilograms, through the Simancas police.

The local authority was alerted by a group of local youth, who said they had spotted an animal that they could not identify, but that appeared to be a species of crocodile crossing the river.

The presence of the animal was also indicated by an agent who, like the group of young people, spotted what appeared to be a large reptile swimming near the confluence of the Douro and Pisuerga rivers when moving to the place.

In the first days of searches, the authorities found some evidence, as part of a devoured fish and possible nests, without being able to identify the animal to which they belonged, but, on Tuesday, 9 June, biologists and scientists from the Chelonia association called for the search completely ruled out this possibility after observation on the spot.

Experts from the non-profit association, which tracks species of crocodiles in different areas of the world, indicated that the fish remains should belong to an otter, since the crocodiles devour them whole and that the nests found did not correspond to this type of reptile.

The searches continued, then, through technical means such as motion detection cameras, thermal cameras, placing baits at various points and a drone to traverse the inaccessible areas of the river, with the purpose of “being able to discard its existence with a higher percentage reliability”.

On 11 June, after no evidence of the crocodile was found over a six-kilometre stretch, between a power plant and a dam, obstacles that experts consider impossible to overcome by the alleged animal.