Switzerland's main waterway link to the sea is barely navigable, with the Rhine so low near the German town of Kaub that the river is almost splitting in two.
Many cargo ships have stopped altogether, and those still moving are carrying only a fraction of their usual loads.
Around 8% of Swiss imports normally travel by the Rhine, including oil products, animal feed and fertilisers.
The Federal Office for National Economic Supply says essential goods will keep reaching the country, but freight is being switched to rail and road at extra cost.
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