The 90ha Étang de Saint-Quentin-en-Yvelines nature reserve provides a habitat for 230 species of nesting and migratory birds such as snipe, ducks and grebes. It was the military engineer Vauban who created this lake at the end of the 17C (after which the new town is named). Today, it offers recreational facilities such as a sailing centre, horse-riding centre and golf course.