No longer a pipe dream for nature lovers on a budget, travel to the Azores' lush forests, lakes, volcanic craters and whale-watching spots has been given a major boost by the debut of low-cost airlines in March.

Since April, the Ponta Delgada airport in the Atlantic archipelago's capital of 250,000 residents has seen 33.6 percent more passengers than the same period last year. The hotel business is booming too, with a 35.2 percent jump in revenues.

Previously, travellers wanting to partake in whale- and dolphin-watching off the Portuguese islands had to travel on far costlier national and regional airlines to reach the Azores.

"I have long dreamt of the Azores. A friend told me about the new low-cost flights and I flew here for 100 euros ($110)," beamed Italian tourist Pamela Massi, 33, marvelling as she watched a group of dolphins playing with the bow of her speedboat in the clear blue water below.

"It really is a special place, and the nature here is beautiful," Massi, an environmental engineer, said off the coast of Sao Miguel, the largest of the Azores' nine islands.

- No mass tourism -

"We were in New Zealand last year, and for two days we looked in vain for whales," said Tineke Intzveld, a Dutch traveller in her 60s.

"Here you see them just 15 kilometres (nine miles) from the coast!" she said, overjoyed to be so near a group of sperm whales, the world's largest toothed predators.

The influx is good news for Futurismo, the company that organises the sea excursions that became a local speciality after traditional whale hunts ended in 1986.

Commercial director Rosa Costa said Futurismo had long been waiting for low-cost airlines to start operating flights to the Azores, though it was "still too early" to measure their impact on a business that already takes in a million euros ($1.1 million) a year.

"But no one here wants the area to become a mass tourism destination. The big challenge will be to set a limit to our capacity and stick to it," said Costa, whose company takes up to 250 people a day out to sea to look for whales, dolphins and turtles.

At just two hours' flight from Lisbon and four from the United States, the Azores were visited by 350,000 people in 2014, making it Portugal's least-frequented region with just 2.1 percent of the southern European country's tourism market.

- 'Niche market' -

While the travel opportunity created by low-cost airlines is a dream come true for many enthusiasts, the influx may ultimately pose an environmental challenge to the islands' pristine natural beauty -- even though locals vow to keep tourism green.

The islands currently have a hotel bed capacity of 10,000, and pending approval from the authorities some 20 new investment projects would soon create 1,800 more. Local leaders have already set the limit at 15,000.

"We caught the wave at the right time because low-cost airlines do a lot of promotion to make their operations profitable," said Joao Reis, days after he inaugurated his Santa Barbara Eco-Beach Resort on Sao Miguel's northern coast.

The 37-year-old invested two million euros in building the resort's 15 hillside villas, using 95 percent recyclable materials including cork coverings, basalt and local woods.

The Portuguese mainland native sees his resort as a sustainable alternative to "a traditional hotel that would destroy the surrounding environment", he said.

With the villas fully booked until the end of the summer, Reis said "the tourism influx should double or even triple in the coming years, but the Azores will remain a niche market" for hikers, surfers and divers.

- 'A calculated risk' -

Local authorities say the islands are ready for the "calculated risk" they face.

"Our environmental protection laws enable us to face the new situation confidently," said local tourism and transport chief Victor Fraga.

For instance, under a two-year-old directive, tourists who want to visit Caldeira Velha's natural hot springs and their emerald green surroundings must pay for access.

Diogo Caetano, who heads the Friends of the Azores association, admits the region and its economy could benefit from tourism development, but he is concerned about "some more sensitive areas, which are now in danger".

The 35-year-old geologist is worried about the panoramic viewpoint overlooking the Sete Cidades lake, where tourists gather to admire two adjacent lakes with completely different colours -- one blue, the other green.

The site's beauty is overshadowed by a massive concrete hotel abandoned in the 1990s, making it a terrible symbol of the destructive building work carried out in the past.

"We must be vigilant so that we ensure that neither the environment nor the idyllic image that attracts tourists is harmed," Caetano said.

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April