A record day on Saturday saw 11 vessels pass through canals carrying 45,000 tonnes of goods to three Ukrainian ports in the Danube delta.
Getting grain out of the three ports, Izmail, Reni and Kiliya, had been regarded as impossible while Russia held the nearby outcrop known as Zmiiny Island, or Snake Island.
Russian troops captured the island in the early stages of the conflict, despite a vulgar rebuke by Ukrainian radio operators that became a symbol of Ukraine's defiance.
But Ukraine announced the recapture of the island in June, while Russia claimed it had withdrawn its garrison as a “goodwill gesture” to ease the grain problems.
Since then, navigation from the Danube to the Black Sea has been restored and more than four million tonnes of grain have left Ukraine by that route, the infrastructure ministry said.
Although the three ports do not have the same capacity as the Black Sea port of Odesa, they have contributed more than other modes of transport such as the railways, it said.
The ministry said shipping traffic to the Danube ports on August 27 was the highest since February 24, the day Russia invaded.
Infrastructure Minister Oleksandr Kubrakov said more investment in the ports could eventually raise their capacity to handle more of Ukraine's grain.
In total, Ukraine's ports processed almost 1.4 million tonnes of agricultural products in July, compared with only 16,500 in March, he said.
That was largely before the standstill in Odesa was lifted under a deal brokered by the UN and Turkey that allowed Black Sea traffic to resume.
Ukraine is one of Europe's most fertile countries and the blockage had led to rocketing food and fertiliser prices and fears of acute hunger for millions of people in developing countries.
Western powers accused Russia of deliberately worsening the situation by bombarding Ukrainian grain warehouses and hoarding its own food supplies.
Ukraine was also in desperate need of the export cash and the Danube was used to ferry some of the goods to ports in neighbouring Romania by barge.
Alternative routes over land could not handle the same volume of grain and faced logistical problems, such as the different width of rail track used by Ukraine and its neighbours in the European Union.