Complex sentence: Access to the footpaths by the river embankments usually gets closed, when the Seine's water level reaches the feet of the Zouave statue, and when the water hits the statue's thighs, the river becomes unnavigable.
Split into simpler sentences: Access to the footpaths by the river embankments usually gets closed, when Seine's water level reaches the feet of the Zouave statue. When the water reaches the statue's thighs, the river becomes unnavigable.