Il n’est jamais aisé de combiner flash et pose longue : j’ai fait de multiples essais entre 1/4 et 6sec mais le bord de la piscine était trop éclairé et « l’effet fantôme » donnait un effet désagréable. Voici la meilleure photo bien que je n’en suis pas satisfait pour autant… La prochaine fois il me faudra deux flashs !
Rgs_ // Régis Matthey - Recherche Graphique & Sociale 
Great idea, well done.
I like to read something more about the setting and the making of, but unfortunately I can´t read the explaining text in french 😦
But nevertheless the photograph is very good.
So this picture was quite challenging because it was hard to mix long exposure with the flash : I got motion blur with a too long exposure. I was expecting to set an exposure over 1s but this part of the swimming pool was too bright. Finally I had to raise the ISO for an exposure of 1/6s.