Perhaps not the perfect tags, but I chose man_made=pier to represent this observation deck.  I added it in changeset #139684720 (see link below)

Respectfully, I doubt it is officially called Dinwiddie Island. Dinwiddie is the name of a first-year residence hall just east of here. Feel free to open a new note if you have a source for its name. Thanks for your understanding!

https://www.openstreetmap.org/changeset/139684720