In a blender, blend blueberries and water until smooth. Pour into a large bowl and mix in whipped topping until smooth.
Mix in ¾ of the blueberries and then pour the mixture into a glass bread pan. (Optional step, line the pan with foil in order tobe able to lift the dessert out of the pan.)
Sprinkle remaining blueberries over the top of the mixture. Freeze for 4-6 hours or overnight before removing from pan or slicing dessert in the pan.