Miles from shore in the open Caribbean Sea, cruise ships are dumping ground-up glass, rags and cardboard packaging.

But vessels in other waters such as the Baltic and North seas are prohibited from throwing any solid waste overboard other than food scraps.

The difference? Many countries with coastlines on the world's most fragile seas abide by a United Nations (UN) dumping ban that requires them to treat ship-generated garbage on land. Caribbean islands, however, have yet to adopt the ban, saying they simply don't have the capacity to treat ship garbage on shore.

They also fear the ban could push ships to dock in less-regulated ports of call.

"We don't have space to take nothing from nobody," said Travis Johnson, assistant harbour master in Saba, an island of 1,500 people that is building a new pier to accommodate larger cruise ships.

The UN's International Maritime Organisation outlawed dumping in 1993 for the Caribbean, a largely enclosed area where the string of islands blocks currents that would flush waste into the Atlantic Ocean. It will not take effect, however, until enough of the surrounding nations report their capacity for treating trash from cruise ships - information that the vast majority of nations so far have withheld.

The UN created the ban to protect areas, vulnerable because of heavy ship traffic or sensitive ecology.

It has already taken effect in the Antarctic, the Baltic Sea, the North Sea and the Persian Gulf and is due to come into force in the Mediterranean in May.

Environmentalists say debris dumped in the ocean can entangle sea creatures, damage water quality and alter ecosystems by providing habitats for opportunistic organisms.

Ignoring the ban also has its consequences for tourism.

Some trash dumped in the ocean washes ashore with the winds and currents, fouling the beaches.

In the Cayman Islands, the government has traced milk cartons on shore to a passing cruise ship.

"If you just dump this out at sea, eventually it gets back up on land," said Jeff Ramos, a Curaçao-based United States Coastguard officer.

In the Mediterranean, environmental officials say coastal nations are highly aware of marine litter and did not resist the ban.

"The issue of garbage from ships is very well-documented, at least in our region," said Lilia Khodjet El Khil, a Malta-based officer with the Regional Marine Pollution Emergency Response Center for the Mediterranean.

Current regulations

Under the current Caribbean regulations, ships can begin dumping garbage, including metal, glass and paper, three miles (five kilometres) from shore as long as it is ground to less than an inch. Almost anything but plastic can be dumped beyond 25 miles (40 kilometres).

The ban, if approved, would outlaw discharging of any solid waste at any distance except for food, which could still be dumped three miles (five kilometres) from shore.

The islands scattered across the Caribbean have struggled to establish a common policy because when it comes to the cruise industry, they see themselves as competitors.

Cruise-ship arrivals are major economic events, with passengers spending roughly US$1.5 billion annually in Caribbean ports. Governments are wary of driving ships away that might find fewer requirements or lower fees elsewhere.