President Recep Tayyip Erdogan speaks at a rally. File photo

President Recep Tayyip Erdogan's dream project of building a canal in Istanbul to rival those at Suez and Panama has turned into a political showdown with the city's new mayor.

Ekrem Imamoglu, who won a shock victory for the opposition in 2019 to become mayor of Turkey's largest city, says the 75 billion lira ($12.6 billion) canal is wasteful, environmentally destructive and could even increase the earthquake risk.

"Canal Istanbul is a criminal project," he tweeted in December as he launched an "Either Canal or Istanbul" campaign and withdrew from a construction protocol signed by the previous mayor.

"We will do everything for this project not to be realised," he told reporters.

This has not gone down well with Erdogan, who has fondly dubbed Canal Istanbul one of his "crazy projects".

First announced when he was prime minister in 2011, it is by far the most complex of a string of new ventures for the city following a tunnel under the Bosphorus, a third bridge across the waterway and a massive new airport.

It envisages a 45-kilometre (28-mile) canal providing an alternative route from the Mediterranean to the Black Sea through western Istanbul, relieving pressure on one of the busiest waterways in the world.

Critics accuse the president of seeking another debt-fuelled, grandiose statement that will benefit his allies in the construction sector at the expense of the environment.

But the president is unfazed by Imamoglu's campaign: "We will build Canal Istanbul whether they want it or not," he said in a speech on Monday. "Turkey has the strength to do it."

Agence France-Presse