Sure looks like fungus, and a bad infection at that.
I have also battled with fungus on maples in my garden. Recently, a granular systemic in addition to foliar sprays have helped. For severely infected trees, putting them in a large grow box where the roots stay COOL and have space to grow is effective. This looks like it may be a well developed tree looking at the ramification, but you need to take action now before it gets away from you.