Turkish President Recep Tayyip Erdogan has finally launched a huge new $15bn scheme to relieve pressure on the vital Bosporus waterway through Istanbul.

Erdogan broke first ground for the Canal Istanbul project at the site of a new bridge in Sazlidere, west of Istanbul, on Saturday.

"Today we are opening a new page in the history of Turkey’s development," the president said, with protestors and supporters both out in force.

"We see Canal Istanbul as a project to save the future of Istanbul... to ensure the safety of life and property of Istanbul’s Bosporus and the citizens around it."

Erdogan has called the canal his "crazy project".

The idea to link the Sea of Marmara and the Black Sea was first mooted in 2011 and revived in 2018.

Mammoth plan

Turkey believes the 45 km waterway will reduce the risk of accidents. Work will take six years and cost $15bn.

Opponents said it will cause ecological damage to the region for little gain.

"Look, this is not a fountain opening ceremony," Erdogan said.

"Today we are laying the foundations of one of the exemplary canals in the world."

The new road bridge over the proposed route of the canal will connect to the North Marmara highway that links other recent infrastructure projects — a new airport and a third Bosphorus crossing, the AP news agency reported.

Istanbul mayor Ekrem Imamoglu was critical of the plan.

"The construction of a bridge here has nothing to do with the canal project. It’s something to do with the road hub,” he told a news conference.

Admirals worried

TradeWinds reported in April that dozens of retired Turkish admirals warned in an open letter that their country’s grand plan to dig a new canal alongside the Bosphorus could threaten the free passage of ships between the Black Sea and the Mediterranean.

Turkish authorities, however, dismissed the letter and detained some of its signatories, claiming that their actions were politically motivated and could be a precursor to a military coup.

Nearly 40,000 ships transit the Bosphorus each year. Given its commercial and military importance, free right of passage through the waterway is enshrined in a 1936 treaty.