A global cruise line company that operates in New Zealand has come under fire in the United States over the use of a controversial technology called “scrubbers”, which is banned in many countries. The Herald spoke to experts, scientists and local authorities about the issue, and about whether New Zealand should be concerned.

As Cyclone Vaianu made landfall across the North Island last month, a giant cruise ship was anchored in the Hauraki Gulf – sparking concern among some Aucklanders preparing for severe weather.

However, the presence of the Discovery Princess was a concern not because of the cyclone but over fears about its chequered record of pollution.

Carnival Corp, the parent company of Princess Cruises, which operates the Discovery Princess and many other cruise ships that sail in New Zealand waters, has been making headlines in Alaska over water pollution concerns.

A report from Alaska Public Media in March revealed that Carnival withheld water pollution data for the Discovery Princess and at least four other ships from Alaskan authorities for months.

The dispute centred around the discharge of exhaust gas cleaning systems, also known as scrubbers.

The relatively new technology has become more prevalent in the industry since global air pollution requirements came into force in 2020, aiming to reduce sulphur emissions.

The Discovery Princess has 1830 cabins and a crew of more than 1300. Photo / Princess Cruises

Some cruise ships have installed scrubbers, which use seawater to remove contaminants from the ship’s exhaust before diluting and discharging wash water into the ocean, as a way to get around the sulphur limits.

Scrubbers allow cruise ships to burn cheaper, sulphur-rich fuel.

However, the system has been criticised for turning air pollution into water pollution, with research showing the process can be toxic to marine life.

Auckland Council lead water scientist Jennifer Gadd, who was the lead author of a 2021 report on the risks from scrubber discharges while at the National Institute of Water and Atmospheric Research (Niwa, now Earth Sciences NZ), says the danger to marine organisms depends on how many of the “petroleum-type products” and metals are discharged.

“The risks are associated with the contaminants that are transferred from the air, which they would be if you didn’t have a scrubber, into the water and also to some extent associated with the bits of engine involved in that scrubber.

“That’s basically some petroleum-type products, polycyclic aromatic hydrocarbons (PAHs), and also some metals. Both those sets of things … can be toxic to marine organisms. But it’s all about how much of it there is.”

An Alaskan inspector discovered “sooty, black globs” from the Discovery Princess’ scrubber discharge point in September last year, with the ship reportedly exceeding United States federal limits.

The revelations from the report in Alaska have sparked concern from environmental experts, with one suggesting Carnival could be “hiding something”.

“Sooty, black globs” were discovered from Discovery Princess' scrubber water discharges. Photo / Alaska Department of Environmental Conservation

Record of pollution

When approached by the Herald, Carnival acknowledged the Alaskan report but insisted “in the US (including Alaska), our scrubbers operate within strict federal washwater limits well over 99.5% of the time and we continuously evaluate ways to improve on this high level of performance”.

“Without a healthy ocean, the cruise industry couldn’t exist. So we work hard to meet or exceed all laws and regulations governing our business, including those protecting and preserving sensitive marine and coastal ecosystems and environments – in New Zealand and everywhere we operate.”

However, Carnival’s record of pollution has continued to come under the microscope in recent years.

Data released by the Southeast Alaska Conservation Council in August last year found 17 of Carnival Corp’s ships reported more than 700 water discharge violations in Alaska in 2023 and 2024.

According to US policy resource centre Good Jobs First, Carnival has racked up more than US$89 million ($151m) in penalties for violations since 2000, including 14 records of environment-related offences of more than US$72m.

Authorities not concerned about Carnival’s issues

Maritime NZ says it is “aware of previous Carnival Corp issues in the US”, but “has no concerns about Discovery Princess being in New Zealand”.

“The Australian Maritime Safety Authority inspected Discovery Princess in January 2026. Under an arrangement known as the Tokyo MOU, maritime regulators in the Asia Pacific region share information from inspections with each other.

“Based on the recent Australian inspection finding no significant issues, Discovery Princess was not inspected again on its arrival in New Zealand.”

Auckland harbourmaster Andrew Hayton and the Port of Auckland echoed similar sentiments about the Discovery Princess and Carnival.

A recent protest against Princess Cruises at Port Chalmers.

‘Like a filter on a cigarette’

Princess Cruises operates four cruise ships calling at New Zealand in the 2025-26 season: Discovery Princess, Crown Princess, Coral Princess and Island Princess.

The Discovery Princess and Crown Princess reported a combined 85 water discharge violations from their scrubbers in Alaska in 2023 and 2024.

Bruce Mahalski, a spokesman for Climate Liberation Aotearoa and Global Cruise Activist Network, believes Carnival is the “worst outfit out there operating”.

“We see scrubbers as just like a Band-Aid, like a filter on a cigarette, to try and make it seem like there’s something that’s being done.”

Dr Timothy Welch, professor of urban planning at the University of Auckland, describes scrubbers as a “loophole”.

“It just takes the sulphur out of the exhaust and dumps it in the water. We’ve basically replaced what’s in the atmosphere and was blocking the sunlight and condensed it down and just started dropping it into the water itself.”

Gadd agrees with those sentiments “to an extent”.

“We’re not really solving a problem, we’re just kind of shifting a problem. But then it’s about which system is the most controllable and how you can deal with the waste the best.”

Environmental risk

The 2021 Niwa report, commissioned by the Ministry for the Environment, sought to understand the environmental risks associated with scrubbers after there was “a bit of concern around it”.

“The risks are really restricted to places where you’ve got less circulation,” Gadd says. “So where the scrubbers are being used in the open ocean or in shipping lanes, there’s really minimal risk, and dilution is the solution in those cases.

“But then when we’re around ports, and particularly harbours that are more enclosed – I think Lyttelton came out as being one that was at the higher end of the risks that we found – that’s where there’s potential for risk.

“But even at those locations, the risks associated with the scrubbers were not that significant compared to all the other issues that some of these harbours already have related to stormwater or industrial discharges and things. So they’re already locations that are, you know, not pristine.”

A cruise ship in Lyttelton Harbour.

Banned in many countries but not in NZ

There are two kinds of scrubbers used by cruise ships: open-loop and closed-loop.

Open-loop scrubbers take gaseous emissions that would have been discharged into the air and funnel them straight into the ocean, while closed-loop scrubbers contain the discharge to be disposed of elsewhere.

“We identified potential risks with open-loop scrubbers when used in ports, including at Lyttelton, and in Akaroa Harbour (associated with cruise ships), but no risks associated with the closed-loop scrubbers, which have lower overall emission rates,” Gadd says.

Discovery Princess and many other Carnival ships use open-loop scrubbers, which have been banned in many countries.

New Zealand has only non-statutory guidance around scrubbers, with the Ministry for the Environment saying that it requests all ships using the systems to “operate closed-loop scrubbers in zero discharge mode and retain any waste on board until it can be disposed of at the next available port reception facility”.

However, that guidance has not been followed by many cruise ships in New Zealand waters.

Industry under the microscope

In a typical year, more than 25 cruise ships visit New Zealand’s coast.

Welch believes the public should be concerned about the industry’s impact on the environment.

“They have a significant impact on the environment, whether it’s water or air.”

He also plays down the often-touted impact on the economy.

“What we do hear a lot about is their contribution to tourism dollars here but … [it’s a] very small impact except for very localised areas overall on our economy, versus the environmental impact that they have nationwide.”

Cruise unique passenger numbers and cruise tourism spending by regions in 2019. Source / Department of Conservation

A 2024 study published by the Department of Conservation on the economic and environmental impact of cruise ships on the Milford Sound, a Unesco World Heritage site, confirmed Welch’s views.

It found that the cruise ship industry was a “niche tourism market in New Zealand, accounting for around 1% of total tourism expenditure”, while the environmental impact and costs were “significant”.

“International research casts considerable doubt upon the economic impacts of cruise tourism and its wider contributions to national and local economies,” it concluded.

“Managing the impacts of cruise tourism can not rely on voluntary commitments and self-reporting. Third-party independent reporting is required to ensure that measurement and mitigation is transparent and publicly reported.”

Mahaski is one of many critics calling for more regulation: “Where do you start with the amount of regulation that still needs to be done on this industry?”

However, the way that cruise ships operate, often by using tax-haven flag states such as Bermuda, the Bahamas and Panama, makes the industry difficult to regulate.

“The way that a lot of these companies work is that a lot of the ships are flagged in countries that are very friendly to lax environmental standards and labour standards,” Welch says.

“So they aren’t heavily regulated in the sense that they mostly spend a lot of their time in international waters, so they don’t really have to comport to any specific standards.

“We’re a small country, so the amount of power we have to foist our own controls on to a huge industry like cruise lines is pretty limited. So we’re a bit beholden to the powers of these huge cruise lines and limited by what we can actually do.”