Greece needs to reduce rampant construction and protect water resources and coastal areas if it wants to maintain a healthy tourism industry across its mountainous mainland and beach-lined islands, the country's ombudsman said in a report on Thursday.

Some 33 million people visited Greece in 2023, 5 million more than a year earlier, drawn by its ancient archaeological sites, turquoise Mediterranean waters and reliably sunny weather.

But in a report released on Thursday, the ombudsman warned of the growing environmental risks and called for urgent reform.

"Our country's economy relies heavily on tourism which makes the need to manage it in a sustainable way even more urgent," the report said. Greece must not "exhaust its potential, wasting it and making our tourist destinations unattractive over time".

Tourism accounts for over a quarter of economic output and nearly 2 million Greeks' annual income derives from the sector, said the report, the first on the sector for the Greek Ombudsman since the authority was founded over 25 years ago.

Revenues are expected to rise to 21 billion in 2024 from 20.5 billion last year - a boon for an economy emerging from a decade-long debt crisis.

Social media favourite Santorini - a small island with 15,550 residents - receives more than 5.5 million visitors annually, twice the number it hosted in 2012, the report said. The island contributes 1 billion euros in annual receipts.

"In Santorini, even tourists complain about the great number of tourists," the report said.

It called for greater regulation to reduce coastal construction and slow the felling of forests which was creating the right conditions for flooding. It also called for greater care of water resources in the face of "huge" requirements for drinking water, swimming pools and water parks.

"Tourism is a field where the lack of vision and strategy emerges with particular intensity. The exercise of a clear tourism governance is an immense need," the report said. (Reporting by Renee Maltezou; Editing by Edward McAllister and Alison Williams)