It looks like sycamore anthracnose, a very common disease that is more common in extended cool, moist springs. Usually it is not too serious, like most foliar diseases, because a new set of leaves is grown next year. It has an effect in proportion to how much green leaf is damaged. You can spray fungicide in early spring but it wouldn't help now. Information on treatment is at http://utahpests.usu.edu/IPM/htm/ornamentals/landscape-insects-and-diseases/anthracnose/.