Turtle

Here is a link to a Spanish Terrapin http://www.euroherp.com/species/Mauremys... , I don't think they look like that either, or like this http://www.iucnredlist.org/details/7717/...
I'll see if there are any other introduced species reported.
This is where I got the information.
http://suite101.com/article/red-eared-sl...

Red-eared Sliders will have the noticeable red patches when they are young. The only time they don't have them is the older, melanistic individuals, which in that case you wouldn't see the yellow lines on the skin either. So this turtle and the turtle you just posted are not Red-eared Sliders because they both have very obvious yellow lines all over the face, and no indication of a red patch.

It actually looks more like a Red-eared Slider, though without the red ears, which is an introduced species and in many places is now more common than either of the local species. Also the location, in the shade of a lot of trees and rarely any sun, is not suitable for the local species which need to keep their body temperature at about 32ºC for optimum performance. Red-eared sliders only need about 27ºC.

Since Graptemys Geographica is endemic to North America I have doubts about them being found in the wild in Spain!

reading from a Turtles of the World book... "these turtles are brightly colored and recall some of the American species. The yellow lines on the neck fade with age, and the carapace becomes uniformly brown to grayish." They wouldn't look out of place in a Florida pond! But going by geography, they are likely Spanish terrapins or an introduced species.