What cruise ships do with sewage
Cruise ships do not dump raw sewage directly into the ocean under normal circumstances. Modern cruise ships are required by international law to treat wastewater before discharge, and most large vessels have onboard treatment systems that process sewage to a standard similar to what a coastal city's treatment plant produces. However, the rules that govern this process vary by location, and enforcement depends on where the ship is operating and which country it is registered under.
The reality is more complicated than a straightforward yes or no. Ships operating in U.S. waters must follow stricter Environmental Protection Agency (EPA) rules than ships in international waters. Ships in some regions dump treated wastewater that meets legal standards but would not be acceptable near a beach. And older ships or those registered in countries with weaker environmental standards may operate with less effective treatment systems than newer vessels.
Key Takeaways
- Cruise ships must treat wastewater before discharge, but the treatment standard depends on where the ship is operating and which country registered it.
- Ships in U.S. territorial waters face EPA rules that require higher treatment standards than international waters allow.
- Treated wastewater is not the same as raw sewage, but it still contains bacteria and nutrients that can harm marine ecosystems.
- Ships can legally discharge treated wastewater in international waters (beyond 3 nautical miles from shore), but discharge closer to shore is restricted or banned.
- Older cruise ships may have less advanced treatment systems than newer ones, and enforcement varies by region.
How onboard sewage treatment works
Most modern cruise ships use one of two main treatment methods: biological treatment systems or advanced oxidation systems. Biological systems use bacteria and microorganisms to break down organic matter, similar to how municipal wastewater plants work on land. Advanced systems use chemicals and ultraviolet light to kill pathogens and break down pollutants.
After treatment, the wastewater still contains dissolved nutrients like nitrogen and phosphorus, which can cause algae blooms in sensitive marine areas. The treated water is not drinking-water quality—it is closer to what a city releases from a treatment plant into a river or bay. Ships discharge this treated water through pipes below the waterline, usually when the vessel is moving and in deeper water where the discharge disperses more quickly.
Some newer ships also have advanced systems that further reduce nutrients and bacteria, but these are more expensive to operate and maintain. Older ships may have simpler treatment systems that meet the legal minimum for their region but produce lower-quality discharge.
What the law requires in U.S. waters
The EPA regulates cruise ship wastewater in U.S. territorial waters—the area within 3 nautical miles of the U.S. coast. In these waters, ships must meet specific standards for bacteria levels and nutrient content. Ships must also keep records of all wastewater discharge and report violations.
Beyond 3 nautical miles, international maritime law takes over. The International Maritime Organization (IMO), a United Nations agency, sets minimum standards for all ships worldwide through the International Convention for the Prevention of Pollution from Ships (MARPOL). These standards are less strict than EPA rules. Ships can discharge treated wastewater in international waters as long as they meet MARPOL standards, which vary depending on the type of wastewater and the ship's distance from shore.
Some states, including Alaska and California, have passed their own stricter rules for ships operating in state waters. Alaska requires ships to use advanced treatment systems and prohibits discharge in certain sensitive areas. California has similar restrictions in some coastal regions.
When ships discharge in international waters
Once a cruise ship leaves U.S. territorial waters and enters international waters (beyond 3 nautical miles), it can legally discharge treated wastewater under MARPOL rules. The discharge must still be treated, but the standard is lower than what the EPA requires. Ships operating in the Caribbean, Mediterranean, or other popular cruise destinations may discharge wastewater that meets international standards but would not be legal in U.S. waters.
The distance from shore matters. Ships can discharge treated wastewater in international waters, but discharge is prohibited or restricted in certain sensitive areas designated by the IMO, such as the Baltic Sea and the North Sea. These areas have stricter rules because they are enclosed or semi-enclosed and do not disperse wastewater as quickly as open ocean.
Enforcement in international waters is weak. Ships are supposed to report discharge to their flag state (the country where the ship is registered), but many countries do not actively monitor or penalize violations. Environmental groups have documented cases where ships disabled pollution-control equipment or falsified discharge records, and penalties when caught are often small relative to the cost of operating proper treatment systems.
The difference between treated wastewater and raw sewage
Treated wastewater is not the same as raw sewage, but it is not clean water either. Raw sewage contains feces, urine, toilet paper, and other human waste. Treated wastewater has had most of the solid material removed and the bacteria reduced, but it still contains dissolved nutrients, some bacteria, and trace chemicals from cleaning products and medications.
The health risk from treated wastewater is lower than from raw sewage, but the environmental impact can still be significant. Nutrients in treated wastewater can cause algae blooms, which deplete oxygen in the water and kill fish and other marine life. Bacteria in treated wastewater can contaminate shellfish beds and make swimming unsafe near discharge points.
A cruise ship with 3,000 passengers and crew produces roughly 30,000 gallons of wastewater per day. Even after treatment, this volume of discharge in a small bay or near a popular beach can harm local ecosystems and water quality.
Gray water and other shipboard discharges
Sewage is not the only wastewater a cruise ship produces. Ships also generate gray water—water from sinks, showers, laundry, and galleys—which is treated separately and often to a lower standard than sewage. Gray water can be discharged in international waters with minimal treatment, and some ships discharge it with only basic filtering.
Ships also produce bilge water (water that collects in the engine room), which can contain oil and fuel residue. Bilge water is supposed to be treated before discharge, but violations are common. Environmental groups have documented cases where ships deliberately discharged oily bilge water at night or in remote areas to avoid detection.
Food waste and other solid waste are supposed to be incinerated or stored for disposal on land, but enforcement varies. Some ships have been caught dumping garbage overboard illegally.
How to find out what a specific cruise line does
Cruise lines publish environmental reports that describe their wastewater treatment systems and discharge practices. These reports are usually available on the cruise line's website under sustainability or environmental responsibility sections. The reports vary in detail—some provide specific information about treatment standards and discharge locations, while others are more general.
The EPA maintains a database of cruise ship violations and penalties. You can search by cruise line or ship name to see if the vessel has been cited for environmental violations. The database is searchable on the EPA website under "Cruise Ship Pollution."
Environmental organizations like Oceana and the Cruise Lines International Association (CLIA) publish reports comparing cruise lines' environmental practices. These reports often rate ships based on the age of their treatment systems, the regions where they operate, and their compliance history.
Frequently Asked Questions
Can cruise ships dump sewage in the ocean at all?
Yes, but only treated sewage, and only under specific conditions. Ships in U.S. waters must meet EPA standards. Ships in international waters can discharge treated wastewater that meets MARPOL standards, which are less strict. Raw sewage discharge is illegal everywhere.
Is treated wastewater safe to swim in?
Treated wastewater is not safe for swimming when ready after discharge. It still contains bacteria and nutrients that can cause illness or algae blooms. The water becomes safer as it disperses and mixes with ocean water, but swimming near a discharge point is not recommended.
Why do some cruise ships have better treatment systems than others?
Newer ships are built with advanced treatment technology that is more expensive but more effective. Older ships may have simpler systems that meet the legal minimum for their region. Ships registered in countries with weaker environmental standards may operate with less effective systems than ships registered in countries with stricter rules.
What happens if a cruise ship violates wastewater rules?
Ships caught violating EPA rules in U.S. waters face fines, which can range from thousands to millions of dollars depending on the violation. Ships caught violating MARPOL rules in international waters may face penalties from their flag state, but enforcement is inconsistent. Some cruise lines have paid large settlements for repeated violations.
Do all cruise lines treat wastewater the same way?
No. Cruise lines use different treatment technologies, and ships operating in different regions must meet different standards. Newer ships generally have more advanced systems than older ones. You can compare cruise lines by checking their environmental reports and the EPA violation database.