Al estanque se le ha muerto
hoy una niña de agua.

Blackburn changes this to a girl drowning in the water, when actually the conceit is far more subtle: "se le ha muerto" means "his child has died." That is, the pond has lost its own daughter, a girl of water. This rises to the level of wtf translation. It's easy to see how the mistake was made: unfamiliarity with this particular syntactic construction, in which the person who loses something becomes the indirect object pronoun rather than the subject of the sentence. Blackburn read it as though it said "En el estanque ha muerto..."

It's too bad, because I'm sure if Blackburn had been alive when the book was being prepared for publication, he would have wanted to show it to someone, get if vetted. There are really simple mistakes in the book, like "sin esfuerzo" (effortlessly) which Blackburn translates as "powerless." I can reconstruct what happened: he read it as "sin fuerza." It's really more of an editing question, because anyone can make mistakes. It is easier to catch other peoples' mistakes, so that even a person with less knowledge of Spanish than I have might be able to catch my errors.

Don't try to tell me that mistakes in translation are felicitous--happy accidents. Usually they aren't.