The main stem of the River Somme passes through Amiens and is generally benign, except during exceptional floods that can last up to several weeks (such as in spring 2001). It is also, on its southeastern outskirts, close to Camon and Longueau, the confluence with its main tributary on the left bank (to the south), and the Avre. The Selle enters from the northwest of Amiens, with two arms (including the Haute Selle) passing behind the Unicorn Stadium, the exhibition park, the megacity and horse racing track, then passing the end of the "Promenade de la Hotoie" and the zoo of Amiens, and to the right of the water treatment plant, in front of the island Sainte-Aragone, opposite the cemetery of La Madeleine in Amiens.