Symbolically, Vijayadasami is the victory of Good over Evil – Goddess Durga annihilating Demon Mahisha and Lord Ram defeating Ravana.
Symbolically, these wars are the prolonged struggle against the ego and ignorance in each human being. After the struggle there is the day of new beginning – Vijaya Dasami.
Goddess Durga Murtis worshipped during Durga Puja are immersed in water on the day.