The Philippines has announced its best-known holiday island Boracay will be closed to tourists for six months over concerns that the once idyllic white-sand resort has become a “cesspool” tainted by dumped sewage.

Philippine President Rodrigo Duterte ordered the shutdown to start on 26 April, his spokesman Harry Roque said on Twitter, without providing further detail.

The decision raises questions about the livelihoods of thousands employed as part of a bustling tourist trade that serves two million guests on the island each year.

Boracay has 500 tourism-related businesses, which had a combined revenue of 56bn pesos ($1.07bn) last year.

But in February Duterte blasted the island’s hotels, restaurants and other businesses, accusing them of dumping sewage directly into the sea and turning it into a “cesspool”.

Officials warned the island’s drainage system is being used to send the untreated sewage into its surrounding turquoise waters.

The environment ministry says 195 businesses, along with more than 4,000 residential customers, are not connected to sewer lines.

Staff work on the drainage system on Boracay Island. Photograph: AFP/Getty Images

In February the government said a total of 300 businesses faced “evaluation” for sanitary or other offences on the 1,000-hectare (2,470-acre) island, of which 51 had already been handed warnings for violating environmental regulations.

Environment undersecretary Jonas Leones said last month a closure would involve having airlines and ferries suspend Boracay services, making the beaches off-limits and stationing police there “if necessary”.

“An iron fist is needed to bring it back to its previous condition. It will be a temporary thing,” Leones said.

The white sands of Boracay, central Philippines. Photograph: Pat Roque/AP

A business association on the island asked the government to shut down only those violating laws.

“It’s unfair for compliant establishments to be affected by the closure,” Boracay Foundation’s Pia Miraflores said.

Miraflores said even before the ban was announced, its shadow had hit some businesses hard in Boracay.

“The tour guides have already complained that they have no more guests. There’s already a huge effect,” she said, adding the quays and jetties were “less crowded” than before.

With more than 500 hotels, Boracay employs 17,000 people, with another 11,000 construction workers working on new projects.