People protest on the Spanish Canary island of Tenerife on March 24, 2012 during a demonstration against plans for petrol firm Repsol to drill for oil off the Canary Islands, which they say threaten tourism and wildlife

Luring millions of tourists a year with its crystal-clear waters, warm winters and precious wildlife, Spain's Canary Islands may hold another treasure—oil—that is attracting a less welcome visitor.

Oil and gas group Repsol aims to begin exploring in 2014 off the archipelago's coast for oil deposits, which could be the largest in Spain.

The group, which awaits only a final clearance from the Environment Ministry, plans to set up a logistical base in January before starting exploration in May at two sites about 60 kilometres (40 miles) offshore.

It is a prospect viewed with dismay by the Canary Islands' regional government and environmental groups.

Opponents of oil exploration have launched a campaign with an online petition titled "Save the Canary Islands", which has more than 35,000 signatures. In 2012, thousands of residents had already joined protests against the project.

The aim is to "internationalise the fight and to bring all the opponents of exploration together under the same campaign," said Fernando Rios Rull, who is helping to run the campaign for the regional government.

Their manifesto, "For an archipelago free of oil", has been signed by more than 40 groups including Greenpeace and the World Wildlife Fund, scientific organisations and Spain's main opposition Socialist Party.

The exploration "represents a serious threat to the natural wealth of the archipelago, to its economy, to its capacity to provide its own drinking water, to its tourism, and thus to its current and future inhabitants," declared the manifesto, read out by actress Pilar Bardem, mother of Oscar-winner Javier Bardem.

A spill would harm tourism for years

Repsol said opposition to its project did not make sense for the economy.

"What country would not want to know the full scale of its natural resources?" asked Repsol spokesman Marcos Fraga.

General view taken on January 30, 2013 of a refinery run by Spanish oil firm Cepsa on the Spanish Canary Island of Tenerife

Especially when its economy, the fourth largest in the eurozone, has been struck by two recessions in the past five years.

"Spain is the OECD country with the greatest dependance on hydrocarbon imports," Fraga said, estimating that Spain imported more than 99 percent of the oil it consumed.

According to Repsol, the deep waters off the Canaries could hold a deposit equivalent to 900 million barrels of oil—or up to 2.3 billion barrels in the most optimistic scenario—which would cover 10 percent of Spanish demand for 20 years, pumping out 100,000 to 150,000 barrels a day.

The group, which has partnered in the project with Australian resources firm Woodside and Germany's RWE, says it could lead to the creation of 3,000 to 5,000 jobs over the same period, good news for a region with a 35-percent unemployment rate.

The project enjoys the firm support of Industry Minister Jose Manuel Soria, a native of the Canary Islands and possible candidate for regional elections in 2015.

He believes oil exploration could "introduce a new economic activity" to the sun-splashed archipelago of seven islands, which lured 10 million visitors in 2012.

General view taken on November 22, 2013 a house on a beach in Playa de Santiago, on the Spanish Canary island of La Gomera

"The white sand beaches on the south of Fuerteventura island are highly prized and tourists come in large numbers in search of sun, clean water and wind," said Miguel Angel Soto, spokesman for Greenpeace Spain.

The neighbouring island of Lanzarote—like the other Canary islands of Gran Canaria and Gomera—has been declared a biosphere reserve by UNESCO and its economy is founded on quality tourism, Soto noted.

"Oil would stain this image and if there was a spill it would compromise tourism on these islands for years," he said, warning of the potentially devastating impact of such an accident in an area inhabited by cetaceans.

But the millions of tourists who visit "get to the Canaries thanks to oil", which fuels their planes and boats, argued Repsol's Fraga, saying had already begun in the neighbouring waters off Morocco and stressing that none of the activity would be visible from the archipelago's beaches.

Repsol, which plans to invest a total of nine billion euros ($12 billion) in the project, aims to explore in the area for one year. If it then requests and receives government authorisation, it would begin extraction. "In about 2019-2020 we would get the first drops," said Fraga.

That depends on oil actually being discovered in sufficient quantity and with sufficient quality, a probability that Repsol puts at about 20 percent.