The destruction of the Kakhovka dam in southern Ukraine has made it impossible to navigate parts of the Dnipro River and deprived Kyiv of an important agricultural export route, shipping authorities said.
The loss of the route is another problem for Ukraine as uncertainty hangs over the future of a UN-brokered deal allowing the safe export of grain from three Ukrainian ports.
Ukraine is an important global grain and oilseeds producer, but its exports have fallen significantly since Russia's full-scale invasion in February 2022.
The navigable Dnipro is traditionally a fast and cheap route to deliver grain and oilseeds, either by barge to Black Sea seaports or directly to consumers using river-sea vessels.
"The Dnipro River is the main artery of river navigation in Ukraine. And the Kakhovka lock was the last Dnipro lock that let all ships out to the open sea," Ukraine's state Shipping Administration said in a statement late on Wednesday.
"In fact, the gateway for Ukrainian exports has been blocked," it said.
About 50 vessels are stranded in the Kakhovka Reservoir, where the water level is falling, and efforts are being made to move them upstream of the city of Zaporizhzhia, the Shipping Administration said.
"Above (Zaporizhzhia) the Dnipro River will remain navigable. Below that, not for a long time yet," it said.
Ukraine was already facing difficulties exporting agricultural products
Three Ukrainian ports were unblocked under the Black Sea Grain Initiative last July but Russia has said the initiative will cease unless an agreement aimed at overcoming obstacles to Russian grain and fertilizer exports is fulfilled.
Ukrainian officials say Russia has since mid-April "unreasonably restricted" the work of the grain deal.
Moscow wants a pipeline that used to take ammonia fertilizer from Russia via Ukraine to be restarted, and said an explosion on it this week would have a negative impact on the Black Sea grain deal.