Cruise ships do dump sewage, but where and how much is heavily regulated
Cruise ships produce thousands of gallons of sewage daily from passenger cabins, galleys, and laundries. Most modern cruise lines treat this sewage onboard using systems similar to municipal wastewater plants, then discharge the treated water into the ocean at least three nautical miles from shore — a practice that is legal under international maritime law. However, the rules vary by location: some ports and countries require ships to pump sewage into shore-based facilities instead, and enforcement depends on which waters the ship is sailing in.
The discharge of treated sewage from cruise ships has been documented for decades, and it remains one of the largest sources of marine pollution from the cruise industry. Environmental groups have pushed for stricter limits, and some regions — particularly around sensitive ecosystems — have begun requiring zero-discharge policies or mandating that ships use approved treatment systems that meet higher standards than the international minimum.
Key Takeaways
- Cruise ships legally discharge treated sewage into the ocean at least three nautical miles from shore under international maritime rules, though some ports require onboard storage or shore-based disposal instead.
- The amount of sewage a cruise ship produces depends on passenger count and voyage length; a large ship with 5,000 passengers can generate 30,000 gallons or more per day.
- Treatment systems vary by ship age and cruise line; older vessels may use basic treatment while newer ships often have advanced systems that remove more contaminants.
- Alaska, the Great Lakes, and some European waters have stricter discharge rules than international law requires, and violations can result in fines for cruise lines.
- Sewage discharged at sea contains treated wastewater but may still carry bacteria, nutrients, and other substances that affect marine life and water quality.
How much sewage does a cruise ship produce
A large cruise ship carrying 5,000 passengers and 2,000 crew members can produce 30,000 gallons of sewage per day or more, depending on voyage length and onboard water use. Smaller ships with 2,000 passengers produce roughly 12,000 to 15,000 gallons daily. This sewage comes from toilets, sinks, showers, laundries, galleys, and medical facilities — essentially the same sources as a small city.
The volume matters because it determines how much treated water enters the ocean and how far from shore the ship must be when discharging. Ships sailing in regulated waters like Alaska or the Baltic Sea often cannot discharge at all during the voyage and must pump sewage into shore facilities at port instead, which means they need onboard storage capacity for the entire journey.
What treatment systems do before discharge
Most cruise ships use one of three treatment methods: advanced wastewater treatment plants, membrane bioreactors, or basic treatment systems. Advanced plants use settling tanks, biological treatment, and sometimes ultraviolet light or chlorination to kill bacteria. Membrane bioreactors use filters to remove solids and microorganisms more thoroughly. Basic systems use settling and chlorination but remove fewer contaminants.
The treated water that leaves the ship is cleaner than raw sewage but is not drinking-water quality. It still contains nitrogen and phosphorus, which can trigger algal blooms in the ocean, and may carry some bacteria and viruses depending on the treatment method used. Environmental testing of discharged wastewater from cruise ships has found fecal bacteria, viruses, and pharmaceutical residues in the water after treatment.
Cruise lines are not required to disclose which treatment system their ships use, and the international standard — set by the International Maritime Organization — allows fairly basic treatment as long as the ship is at least three nautical miles from shore when discharging.
Where discharge is allowed and where it is banned
Under international maritime law, ships can discharge treated sewage anywhere beyond three nautical miles from shore. However, many regions have stricter rules. Alaska bans discharge of treated sewage within state waters entirely, requiring all cruise ships to pump sewage into shore facilities at ports like Juneau and Ketchikan. The Great Lakes prohibit discharge of any sewage, treated or not. The Baltic Sea, Mediterranean, and North Sea have regional agreements that limit discharge or require ships to use approved facilities.
Some individual ports also impose their own rules. The Port of Los Angeles requires cruise ships to use shore-based sewage facilities, and several Caribbean ports have begun requiring zero-discharge policies to protect coral reefs and tourism. When a ship enters these waters, it must comply with local law or face fines and potential detention.
The challenge for cruise lines is that rules change by region, so a ship sailing Alaska one month and the Caribbean the next must switch between discharge and no-discharge modes. This is why many modern cruise ships are built with large holding tanks — to store sewage when discharge is prohibited and pump it at ports where it is allowed.
Violations and fines for illegal discharge
Cruise lines have been caught illegally discharging sewage or falsifying discharge records. Royal Caribbean paid a $27.5 million settlement in 2016 for dumping oily waste and sewage in U.S. waters and lying about it in official logs. Carnival Corporation agreed to a $40 million settlement in 2017 for similar violations across multiple ships. These cases revealed that some crew members were deliberately bypassing treatment systems or discharging in restricted waters and then falsifying records to hide it.
The U.S. Coast Guard and Environmental Protection Agency monitor cruise ship discharge through port inspections and at-sea observations. Violations can result in fines, criminal charges for crew members, and mandatory installation of better treatment systems. However, enforcement is limited by the number of ships and the difficulty of detecting violations at sea.
What happens to sewage pumped at port
When a cruise ship pumps sewage into a shore-based facility — which is required in Alaska, the Great Lakes, and some other ports — the sewage goes into the municipal wastewater system. This means it is treated at a land-based plant, which typically has more advanced treatment than shipboard systems and is subject to stricter environmental standards.
However, not all ports have adequate sewage infrastructure. In some Caribbean and developing-world ports, shore-based facilities may be limited or outdated, and sewage may be treated less thoroughly than it would be on a modern cruise ship. This is why some environmental groups argue that requiring shore-based disposal in poorly equipped ports can actually increase pollution rather than reduce it.
Environmental impact of cruise ship sewage
Sewage discharged from cruise ships contributes nitrogen and phosphorus to the ocean, which can cause eutrophication — a process where excess nutrients trigger algal blooms that deplete oxygen and kill fish and other marine life. Treated sewage also carries bacteria and viruses that can affect marine ecosystems and contaminate shellfish beds, which are sometimes closed to harvesting after cruise ship discharge.
The impact is concentrated in popular cruise destinations where multiple ships discharge in the same waters on the same day. Areas like the Caribbean, Mediterranean, and Alaska see hundreds of cruise ship visits per season, and the cumulative effect of sewage discharge from all those ships is significant. Coral reefs near cruise ports show higher levels of disease and algal overgrowth compared to reefs in less-visited areas.
Some cruise lines have begun installing advanced treatment systems that exceed international standards, partly in response to environmental pressure and partly because stricter regional rules are becoming more common. However, older ships with basic treatment systems remain in service, and retrofitting them is expensive.
Frequently Asked Questions
Is cruise ship sewage treated before it goes into the ocean?
Yes, cruise ships are required to treat sewage before discharge, but the level of treatment varies. Most ships use systems that remove solids and kill some bacteria, but the treated water still contains nutrients and may carry some microorganisms. Treatment standards are set by international maritime law and vary by region.
How far from shore do cruise ships have to be to dump sewage?
Under international law, at least three nautical miles from shore. However, many regions require greater distances or ban discharge entirely. Alaska requires zero discharge in state waters, and some ports require ships to pump sewage into shore facilities regardless of distance from shore.
Can you get sick from swimming near a cruise ship?
The risk depends on when and where the ship discharged. If discharge occurred recently in the area where you are swimming, there is a higher risk of exposure to bacteria or viruses. Beaches near busy cruise ports sometimes issue advisories after heavy cruise traffic, and some shellfish beds are closed to harvesting after cruise ship discharge.
Do all cruise lines treat sewage the same way?
No. Newer ships and lines that have invested in advanced treatment systems remove more contaminants than older ships with basic systems. Cruise line websites do not always disclose which treatment method their ships use, so you may need to contact them directly if this is a concern for you.
What happens if a cruise ship is caught dumping illegally?
The ship can face fines, detention at port, and mandatory installation of better treatment systems. Crew members involved can face criminal charges. However, enforcement depends on detection, which is difficult at sea, so violations are not always caught.