Most books use the term "swim lane", but some articles use the term "swimlane" (for example, https://support.office.com/en-us/article/Add-swimlanes-to-a-flowchart-D794B112-8AA3-4360-8F12-E38BC62AD558). Is this correct?
Such noun + noun collocations are very common in Germanic languages, and English is a Germanic language.
When the collocation becomes used "often enough" — and who is going to be the judge of that but the individual speaker? — you will start to see the nouns presented as a single "word" on the printed or written page, or perhaps with a hyphen separating the nouns, swim-lane.
Anyone who tells you that swimlane is wrong, or that swim lane is wrong, or that swim-lane is wrong, or that one or the other of them is "the right way", is wrong.
Any literate native speaker will understand that those three different ways of referring to the thing all refer to the same thing.