A trip with a bizarre end

Last week I went to 'La Gola', just next to the mouth of the Fluvià river. Me and my mother went with the dogs for a walk, but as always, my dogs get lost. This time we went fot the walk too late, because in the winter the night falls very early compared with the summer.

We have GPS that locates them, they were at 500m away from us, inside a giant cane field. We shouted and shouted them, but they didn't want to come. The night fell, and my father came to help us, but they didn't want to come anyway.
Me and my father decided to pierce the field and go find them, but is was impossible, it was too brushy, and wild pigs live there so we were scared.
Finally, we decided to drive to ther other side of the field going around, through the highway to Castelló d'Empúries. We turn right, into Càmping Nautic Almata, and in the middle of the brushes, we found my dog that was stucked there. The other one is younger and came runing towards us.

Fortuanetly, nothing happened, but the strange thing is that my old dog (to ariive at that place wehre he was stucked), had to pass a river to get ther, it's impossible.

At the beggining (where we first lost them) is in the red spot
We found them at the green spot 

How is possible they could swim the river marked with maroon?
It's a big river not a joke.