I'll help you get across a river.
Once unrecognised in Fischer's song,
Later I found fame alone
And also as a US state.
Who am I?
Concentrate on lines 1, 3, and 4. Line 2 and the title should be used only as checks to ensure your answer is right. They're there to make sure the answer is unique, and the way they fit it is rather twisted (but should become clear once you have the right idea).
The answer is not actually a US state.
To be accepted, an answer must explain all lines including the title. But any serious attempt at a solution will get an upvote from me.