ATHENS — Greenpeace on Wednesday renewed calls against proposed deep-sea oil and gas exploration off southwest Greece, warning of “unbearable” consequences to endangered Mediterranean whales and dolphins.

Greenpeace Greece official Kostis Grimanis said the project should be scrapped before “it starts to wreck the Mediterranean.”

The appeal came as the environmental group published new research on sea mammal populations in parts of the miles-deep Hellenic Trench, including areas that would be affected by prospecting.

The three-week summer project, in cooperation with the Athens-based Pelagos Cetacean Research Institute, detected 35 endangered sperm whales and dozens of dolphins — some threatened — in depths of up to 4,200 meters (13,800 feet).

Greenpeace said sound-sensitive cetaceans — whales and dolphins — would be at risk from the deafening sonic blasts used in undersea prospecting. Greek officials counter that strict environmental safeguards will be observed.

In 2019, Greece granted exploration rights for two blocks of seabed south and southwest of the island of Crete to a consortium of energy companies TotalEnergies and ExxonMobil with Greece’s Hellenic Petroleum. Environmentalists had protested at the time, also highlighting the potential risk of spills from deep-water drilling. Prospecting has not yet started, and it’s unclear when it will — although the concession states that it must be in the winter, to less impact cetacean breeding periods.

Greenpeace’s Grimanis said the project means “exposing endangered species and crucial ecosystems to unbearable noise and pollution from seismic blasts and deep-sea drilling operations.”

“And for what? To keep burning oil and gas, one of the dirtiest and most expensive energy sources, when the climate crisis demands we urgently walk away from them.”

The Hellenic Trench includes the Mediterranean’s deepest waters, at 5,267 meters (17,300 feet) and is a vital habitat for the sea’s few hundred sperm whales, and for other cetaceans already threatened by fishing, collisions with ships and plastic pollution.

These mammals are particularly sensitive to the underwater noise produced by seismic surveys for fossil fuels, in which sound waves are bounced off the seabed to locate potential deposits. Sonar used by warships has been shown to have deadly effects on whales, and experts say seismic surveys can do the same.

Greece is hoping to raise revenues and achieve greater energy security through offshore oil and gas, and the issue of undersea exploitation rights has further poisoned relations with neighboring Turkey which claims large parts of the Eastern Mediterranean as its own.

Nevertheless, a Greenpeace statement Wednesday urged Athens to “immediately” cancel “all fossil fuel plans.”

“Any new investment in the falsely advertised ‘good’ fossil gas will in a few years become a stranded asset with dire consequences for the economy … and the country’s natural resources,” it said.