1. not passable; not allowing passage over, through, along, etc.: Heavy snow made the roads impassable.
2. unable to be surmounted: an impassable obstacle to further negotiations.
There has been a lot of hype this year citing data which is suggesting that we’ll be able to navigate the Northwest Passage and some even so bold as to suggest a completely ice free Arctic Sea. You could say: “A picture is always worth 1000 data points.”
I’d say “impassable” fits this picture pretty well:
Image rotated- click for source image. Credit: Terra/MODIS true color
Some reference views to help you get your bearings, here is what the area would be like if “ice free” as some folks are predicting to happen this summer:
And here is the overall photo area with more familiar landmasses visible: