WASHINGTON — Water, water everywhere, but where does the wastewater go?

Critics of the cruise ship industry say the Environmental Protection Agency and the Coast Guard don't do enough to regulate the disposal of millions of tons of waste generated annually.

This is hardly the kind of thing you want to think about when you ship out on the high seas on one of the thousands of adventures the cruise industry sold last year. But as the worldwide cruise ship fleet has grown to some 230 vessels, carrying up to 5,000 passengers, the volume of waste has grown along with it.

Cruise Lines International Association, a marketing group for the industry, said 10.6 million people set sail on a cruise in 2004, an 11 percent increase from the previous year.

In a week, a large ship (carrying 3,000 or more) can generate 210,000 gallons of sewage, also known as black water. An additional 1 million gallons a week of so-called gray water — wastewater from laundries, sinks and showers — can also be produced, plus quantities of hazardous waste, solid waste and oily bilge water.

A patchwork of federal regulations and international agreements govern how waste must be treated before it is discharged from a cruise ship. States also can impose "no discharge" zones with EPA approval.

Ships may discharge treated sewage within three nautical miles of shore; outside that boundary, they can dump raw sewage. Gray water is not considered sewage and can be disposed of anywhere.

The cruise industry said it has additional voluntary policies to rid ships of waste safely, such as not discharging untreated gray water within four miles of shore. But environmental groups have been pressing the EPA to regulate more stringently and for cruise lines to update their current treatment systems.

"The public is not aware of all the problems with cruise ships. It's a classic polluting industry that has little oversight from regulators who should be cracking down on them," said Russell Long, vice president of the Bluewater Network, an environmental group.

The industry said it has cleaned up its act since some prominent cruise lines were hit with major fines in the late 1990s for polluting. "That served as a wake-up call to the cruise industry," said Michael Crye, president of the International Council of Cruise Lines, which represents 16 cruise line companies. "We took steps to exceed environmental laws and procedures from all over the world."

Ross Klein, professor of social work at Memorial University of Newfoundland who runs a Web site called Cruisejunkie.com, said the industry works at projecting a clean image, but the lack of monitoring makes it tough for regulators to pin down violations.

Most cruise ships are equipped with marine sanitation devices to treat sewage. The EPA sets their performance standards, and the Coast Guard oversees the design, installation and operation of the devices as part of its overall vessel inspections.

The Coast Guard administered 185 compliance exams last year, down from 246 in 2000.

"The solution to the problem is to make some rules these guys have to follow. This is the 21st century. We need to update to state-of-the-art advanced treatment devices," said Jackie Savitz, director of an anti-pollution campaign run by Oceana, an international ocean conservation organization.