I’m up the creek without a clue – help!

Portsmouth in 1717 (from William Gates History of Portsmouth, 1900)

NOSTALGIA: A seed of learning planted 300 years ago that’s blossomed into Portsmouth Grammar School

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What is the correct spelling for the creek that runs between Portsea Island and the rest of England?

I have a photograph taken at Hilsea with the caption ‘The new bridge at Portscreek’.

Then I have a photo of a signal box there which bears the nameplate Portcreek Junction. I have yet another with the caption which splits the word so it becomes Port Creek. Yet another states ‘New bridge of Ports Creek’. I like to spell it Portscreek, but can anyone tell me the definitive way to spell it?