The cost of rebuilding in Greece after last year's destructive floods, which killed 17 people and destroyed essential infrastructure, will exceed three billion euros ($3.2 billion), the prime minister said Tuesday.

In September, Storm Daniel, a Mediterranean cyclone of unprecedented intensity, unleashed months' worth of rain in just hours on Thessaly, Greece's most fertile plain.

Another storm, Storm Elias, followed just weeks later.

Combined the two storms triggered what Prime Minister Kyriakos Mitsotakis later called the worst floods in Greek history.

"The overall rehabilitation of the damage caused by Daniel and Elias will exceed three billion euros," Mitsotakis said during Tuesday's visit to Thessaly.

Just repairing the area's roads, rail network, and schools will cost 1.4 billion euros, he added.

"The road network will be rebuilt better than before," Mitsotakis vowed, adding that the repaired rail network will be delivered by the end of 2025.

The deluge destroyed roads and bridges and drowned tens of thousands of farm animals.

Some of the plans under consideration have drawn criticism from environmental groups, especially the proposals made by HVA, a Dutch company advising the Greek government.

Greenpeace, WWF, the Hellenic Society for the Protection of Nature, and the Hellenic Ornithological Society last week said the main focus was an "old-school" dam construction instead of eco-friendly river management, favoured by the EU.

The groups on Thursday criticised proposals to dredge rivers, arguing that removing obstacles helps floodwaters flow even faster.

There are also fears that the reconstruction will revive decades-old plans to divert the Achelous River in western Greece, a project repeatedly struck down by the country's top administrative court.

In a statement sent to AFP, HVA insisted that its approach was science-based.

The company noted that nature-based solutions have been examined under several EU initiatives, but there is "insufficient knowledge" as to whether they apply to projects of the size required in Thessaly.