Turkish President Recep Tayyip Erdogan on June 27 launched the start of construction of the controversial Kanal Istanbul mega infrastructure project that critics say has little practical benefit and could cause great environmental harm.

The project has an estimated cost of $65bn. Most of Turkey's leading banks have said that they will refuse to finance the canal, stating that they are tied to international commitments to only support environmentally sustainable projects. Observers have claimed that with Turkey sunk in economic crisis, the project will be used to generate fresh revenues for business people that back Erdogan’s ruling AKP party.

The gigantic 45-kilometre (28-mile) waterway sliced through Istanbul would run parallel to the Bosporus Strait that connects the Black Sea to the Sea of Marmara and the Mediterranean.

"Today we are opening a new page in the history of Turkish development," Erdogan said during the ceremony to lay the foundation stone of a bridge forming part of the project. The first project construction work will see the building of Sazlidere bridge, which will stretch over the canal.

Citing the risks posed by the rising number of ships passing through the Bosporus, Erdogan claimed the project was mostly aimed at "ensuring the safety of citizens in Istanbul" and allowing the country to take "a more important place" in international trade.

Dismissing critics, he said: "All stages of the project have been designed in accordance with science."

Istanbul’s opposition mayor, Ekrem Imamoglu, has voiced alarm about the project. "I am sweating when I talk about this channel, because I can feel this is a nightmare, I can feel it deep inside," he said, as reported by VOA. "Because I listened to tens of briefings from the scientists who are all warning against it,” he added.

Imamoglu warned that the project threatens the city's water supplies and risks wider environmental consequences in the region's delicate balance of interconnected seas.