"impassable by" is a correct and usable phrase in written English
It is typically used to describe something that cannot be crossed or overcome by something or someone. Here is an example: "The river was impassable by foot, so the hikers had to find an alternate route."
Covered by ice, nearly impassable by ship, the Arctic is still earth's least-explored frontier.
Dawn on June 15 found them at the Chickahominy River, close to safety but rendered impassable by spring rains.
Guanajuato remains resolutely a walkers' city, with not a straight street to be found, and most are impassable by car.
Northwestward from the latter the plateau continues to fall toward the Qattara Depression (Munkhafaḍ al-Qaṭṭārah), which is uninhabited and virtually impassable by modern vehicles.
But defenders of the agency said it was hardly the paramedics' fault that so many streets were left unplowed and impassable by ambulances for days.
The streets were unpaved and impassable by any kind of vehicle, a river of muck trickling down a gully in the center of one.
Poppies sprout fast: a first crop will be harvested by the end of April; a second will be ready in June.Iran has strengthened security along a border already crawling with soldiers and paralleled by immense trenches, impassable even by a self-navigating camel with a bellyful of drugs.
The Rhodesians, meanwhile, were led into impassable country by a local guide, and swiftly retreated after being attacked by German bombers.
Much of the northeast was impassable, and by late Saturday rescuers had not arrived in the worst-hit areas.
In late January 1910, all of these things demanded Lépine's attention as floodwater rendered entire sections of Paris impassable except by boat or makeshift walkway.
There are too few sidewalks in Dhaka, and those that exist are often impassable, occupied by vendors and masses of poor citizens who make their homes in curbside shanties.
