1999, Robert D. Abbott, The World as Information: Overload and Personal Design, ISBN978-1871516753, page 38:
There is what appears under normal circumstances to be an uncrossable boundary, a total barrier.
2009 August 16, Max Byrd, “Rosie and Friends”, in New York Times:
And it’s brilliantly stitched together by motifs of chrysalises and movies and by a joyous abundance of metaphor and simile: “the ding of a bicycle bell like struck crystal”; a woman “talking for much of the day in a steady soft uncrossable stream.”
2009 August 24, Rita Campbell, “Father and young son die in loch tragedy”, in The Press and Journal:
There are very few bridges on the footpaths in Skye and even short periods of heavy rain can cause rivers to rise rapidly, often making them uncrossable.