Cruise ships do dump some sewage at sea, but not the way most people imagine

Cruise ships generate roughly 150,000 gallons of sewage per day from toilets, sinks, showers, and galleys. Most of this sewage is treated onboard in the ship's wastewater treatment plant before discharge. However, treated wastewater is still released into the ocean in international waters — that is legal under international maritime law. The rules about where, when, and how this happens depend on whether the ship is in port, in coastal waters, or in the open ocean.

The key distinction is between treated sewage (which ships can discharge almost anywhere) and untreated sewage (which is heavily restricted). Most modern cruise ships treat their sewage to a standard that meets or exceeds international requirements. But treatment does not mean the water is clean enough to drink — it means solids have been removed and the water meets discharge standards set by the International Maritime Organization (IMO) and the U.S. Environmental Protection Agency (EPA).

Key Takeaways

  • Cruise ships treat most sewage onboard before releasing it into the ocean, but treated wastewater discharge is still legal in international waters under IMO rules.
  • Ships must hold sewage in tanks and cannot discharge within 3 nautical miles of U.S. coastlines, and within 12 nautical miles in some other countries.
  • Untreated sewage discharge is illegal in U.S. waters and most coastal zones, and violations result in significant fines and criminal penalties.
  • Cruise lines have been caught illegally dumping untreated sewage multiple times, leading to settlements and increased EPA monitoring.

What happens to sewage onboard a cruise ship

When you flush a toilet on a cruise ship, the waste goes into a holding tank, not directly overboard. From there, the sewage enters the ship's wastewater treatment plant, which is essentially a miniature version of a municipal treatment facility. The plant uses a combination of physical separation (screening and settling), biological treatment (bacteria that break down organic matter), and sometimes chemical treatment to reduce solids and pathogens.

After treatment, the water is tested and then discharged through a pipe that extends below the waterline. The discharge happens continuously while the ship is moving in international waters, or it may be stored in tanks if the ship is in restricted coastal waters. Some cruise lines advertise advanced treatment systems that produce water clean enough to meet drinking water standards, though this water is still discharged rather than stored.

Where cruise ships can and cannot dump sewage

The rules change depending on how far the ship is from shore. In U.S. waters, ships cannot discharge any sewage within 3 nautical miles of the coast — roughly 3.5 miles. Between 3 and 12 nautical miles, ships can only discharge treated sewage that meets EPA standards. Beyond 12 nautical miles, the rules are set by the IMO, and treated sewage discharge is permitted.

Other countries have stricter rules. The European Union requires ships to hold all sewage in tanks while in EU waters and discharge only in designated reception facilities in ports. Canada prohibits discharge within 12 nautical miles. These variations mean a cruise ship operating in the Caribbean follows different rules than one in the Mediterranean or Alaska.

When a ship is docked in port, sewage must be pumped into the port's shore-based treatment facility, not discharged into the harbor. This is where you see the large hoses connected to cruise ships at the dock — those are sewage lines, not water lines.

How often cruise ships have illegally dumped sewage

Despite the rules, cruise lines have been caught deliberately dumping untreated sewage and falsifying records. In 2016, Royal Caribbean pleaded guilty to deliberately dumping oily waste and untreated sewage into the ocean and lying about it in official logs. The company paid a $40 million settlement and agreed to enhanced monitoring. In 2019, Carnival Corporation (which owns Carnival, Princess, and Costa cruise lines) paid $20 million for similar violations spanning years.

These cases revealed a pattern: crews were bypassing treatment systems to save time and money, and officers were falsifying the ship's oil record book — the official log of all waste discharges. The EPA and Coast Guard now conduct unannounced inspections of cruise ships and review their waste logs. Violations can result in criminal charges against individual crew members and officers, not just fines against the company.

The difference between treated and untreated discharge

Treated sewage that meets IMO standards still contains bacteria, viruses, and nutrients that can harm marine ecosystems. It is not the same as raw sewage, but it is not clean water either. The treatment removes most solids and reduces pathogens, but some remain. When discharged in large volumes in the open ocean, the impact is diluted. When discharged illegally in coastal waters or harbors, the concentration is much higher and can cause algal blooms, dead zones, and beach closures.

Untreated sewage — the kind that bypasses the treatment plant entirely — contains all the original pathogens, parasites, and nutrients. Dumping this in coastal waters is a public health hazard and is illegal in U.S. waters and most other jurisdictions. The fines and criminal penalties reflect how seriously this is treated.

What cruise lines say about their sewage systems

Most major cruise lines now advertise their wastewater treatment systems as a selling point. Some claim their systems produce water that meets or exceeds drinking water standards. Others highlight advanced technologies like membrane bioreactors or ultraviolet disinfection. These claims are generally accurate — the technology exists and works. However, the water is still discharged into the ocean rather than stored or used onboard, so the quality standard is not the limiting factor.

Cruise lines are also required to publish their environmental policies and disclose their waste management practices. You can find these on their websites. Some lines have committed to zero discharge in sensitive areas like Alaska or the Caribbean, meaning they hold all sewage in tanks and pump it ashore in port. Others have committed to using only shore-based reception facilities in certain regions.

What you should know as a cruise passenger

The sewage from your cabin is treated before discharge, and discharge in international waters is legal. However, the legality does not mean there is no environmental impact — treated sewage still affects marine life and water quality. If environmental impact concerns you, you can choose cruise lines that have committed to stricter practices, such as zero discharge in sensitive areas or use of advanced treatment systems.

You can also report suspected illegal dumping. If you witness a crew member dumping waste overboard or falsifying logs, you can report it to the EPA, the Coast Guard, or the cruise line's corporate office. The EPA has a hotline and online reporting system for maritime pollution. Past cases have been cracked by crew members and passengers who reported what they saw.

Frequently Asked Questions

Is treated sewage discharge the same as dumping raw sewage?

No. Treated sewage has had solids removed and pathogens reduced through biological and chemical processes. Raw sewage is untreated waste. Treated discharge is legal in international waters; raw sewage discharge is illegal in U.S. waters and most coastal zones. However, treated sewage still contains some bacteria and nutrients that can affect marine ecosystems.

Can I get sick from swimming near a cruise ship?

Cruise ships do not discharge sewage while docked in port — it goes into shore facilities. In international waters, treated sewage is diluted across a large area. The risk of illness from cruise ship discharge is low in open ocean but higher in enclosed bays or harbors. Beaches near cruise ports are sometimes closed due to high bacteria levels from multiple sources, not just cruise ships.

What happens to sewage when a cruise ship is in port?

All sewage is pumped into the port's shore-based treatment facility through large hoses connected to the ship. The port facility then treats the sewage using the same methods as a municipal wastewater plant. Ships cannot discharge sewage into the harbor or bay.

How do I know if a cruise line has been caught dumping illegally?

You can search the EPA's enforcement database online or check news reports. Major violations are usually reported in maritime and environmental news outlets. You can also contact the cruise line directly and ask about their environmental record and current waste management practices.

Do all cruise ships have treatment plants?

Yes. International maritime law requires all ships to have wastewater treatment systems that meet IMO standards. Older ships may have older systems, but they must still meet the minimum standard. Newer ships often have more advanced systems, but the legal requirement is the same for all.