As part of their normal activities, vessels may discharge a wide range of wastes and contaminants into U.S. and international waters, including nutrients, pathogens, oil and grease, metals such as copper, toxic chemical compounds, and non-native aquatic nuisance, or invasive, species (AIS). The discharges can include shower and laundry facility water, deck washdown and runoff, bilgewater, motor fuel, machinery wastewater, and ballast water, among others. Contaminants in these discharges can have a broad array of effects on aquatic species and human health, many of which can be harmful. Similarly, the universe of vessels that may release these discharges is diverse and includes commercial fishing vessels, cruise ships, ferries, barges, mobile offshore drilling units, tankers, cargo ships, container ships, research vessels, and emergency response vessels, such as firefighting and police vessels. Including recreational vessels, the universe of vessels is in the millions. Ballast water discharges from vessels have been a particular concern, because invasive species entering U.S. waters cause social, recreational, and ecological disturbances and result in significant economic losses. National attention was drawn to the invasive species problem with the arrival of zebra mussels in the Great Lakes in the late 1980s. Since then, virtually all coastal and Great Lakes states have experienced ecological change and loss from AIS. For example, zebra mussels attach to hard surfaces such as water intake pipes that are used for cooling water and municipal water supply. When this occurs, the infestation can cause significant reduction in pumping capacity and occasionally has caused plant shutdowns. Ballast water has been identified as a major pathway for introduction of AIS. Ships use large amounts of ballast water to stabilize the vessel during transport. Ballast water is often taken on in the coastal waters in one region after ships discharge wastewater or unload cargo. It is then discharged at the next port of call, wherever more cargo is loaded. The practice of taking on and discharging ballast water is essential to the proper functioning of ships, because the water that is taken in or discharged compensates for changes in the vessel's weight as cargo is loaded or unloaded, and as fuel and supplies are consumed. However, ballast water discharge typically contains a variety of biological materials, including non-native, nuisance, exotic species. If these species are released into lakes or rivers as part of ballast water discharge, they can alter aquatic ecosystems. Today stakeholders broadly agree on the need for strong measures to control vessel discharges, especially ballast water discharges, but there are differing views on how to do that. Vessel discharge requirements in the United States are a result of U.S. Coast Guard regulations; a U.S. Environmental Protection Agency (EPA) permit; and individual state rules, limitations, and requirements. Vessels also are subject to a number of international agreements, in particular to Conventions adopted by the International Maritime Organization (IMO), which apply to vessels operating under flags of countries that are Parties to the Conventions. This report discusses the combination of regulations and standards, which is at issue today and is addressed in legislation in the 114 th Congress, the Vessel Incidental Discharge Act ( S. 373 , H.R. 980 , and titles included in S. 1611 , S. 2829 , and H.R. 4909 , which the House passed on May 18). Federal authority to address ballast water concerns in the United States is contained in the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990 (NANPCA, P.L. 101-646 ), as amended by the National Invasive Species Act of 1996 (NISA, P.L. 104-332 ), and is administered by the Coast Guard. Initially this authority required a program to prevent the introduction and spread of invasive species into the Great Lakes by managing vessel ballast water discharge, a program that subsequently was extended to all U.S. ports and waters. Ships that have operated outside the U.S. Exclusive Economic Zone were directed to undertake high seas ballast exchange before entering U.S. waters. However, ballast water exchange is understood to be only partially effective to reduce the spread of aquatic organisms and pathogens and is often not carried out due to safety considerations that are dependent on weather and sea conditions. In 2012 the Coast Guard promulgated a rule establishing new requirements for ballast water management. The Coast Guard amended its requirements to include numeric standards that establish allowable concentrations of living organisms in ballast water discharged in U.S. waters. It also established numeric limits on human health indicator microorganisms, such as intestinal pathogens. (See the text box on page 4 .) The rule applies to all U.S. and foreign vessels equipped with ballast tanks and operating in waters of the United States, unless specifically exempt. The Coast Guard estimated the number to be 3,046 vessels over a 10-year period. Under the rule, the standards would apply to new vessels—meaning those constructed on or after December 1, 2013—on delivery and would apply to vessels constructed before December 1, 2013, according to a phased schedule beginning January 1, 2014, depending on a ship's ballast water capacity. Under the Coast Guard rule, vessel owners and operators have several compliance options. They can eliminate ballast water discharge. They can discharge to an onshore facility or to another vessel for the purpose of treatment. They can use ballast water that is only drawn from a U.S. public water system. They can install a ballast water management system that has been approved by the Coast Guard. For this option—installation of treatment technology—the rule details procedures for land-based and shipboard testing and Coast Guard approval. The numeric standards in the Coast Guard rule overlap with standards specified in a 2004 Convention of the IMO. Like the Coast Guard rule, the IMO ballast water performance standard identifies organisms of various sizes and also identifies concentrations of human health indicator microbes in ballast water that management systems are required to achieve prior to discharge. The numeric standards in the Coast Guard rule and the IMO Convention are the same. EPA also has authority to regulate vessel discharges, including ballast water, but for many years the agency mostly chose not to do so. This authority stems from the Clean Water Act (CWA), which prohibits the discharge of pollutants from a point source into U.S. waters without a permit. Vessels are defined in the statute as point sources. In 1973, EPA promulgated a regulation that excluded discharges incidental to the normal operation of vessels—including ballast water (but not including vessel sewage discharges, which are regulated)—from CWA permitting requirements. EPA's position was that, because vessels are mobile and move between jurisdictions, the traditional CWA mechanism of regulating through state-issued permits is problematic, because state requirements can vary widely. This long-standing regulation was challenged in federal district court by environmental advocacy groups who wanted EPA to address ballast water as a source of AIS in U.S. waters. The court found that the 1973 regulation contradicted Congress's intention that discharges from vessels be regulated under the CWA, and it vacated, or revoked, the regulatory exclusion. In 2008, this ruling was upheld. EPA initially estimated that the court's ruling could affect and would require permits for as many as 98,000 commercial fishing, passenger, cargo and other vessels, plus over 13 million recreational boats. Congress responded to that estimate by enacting two bills to restrict the population of vessels subject to regulation. The first, the Clean Boating Act of 2008, provided a permanent exemption from CWA permitting requirements for discharges incidental to the normal operation of recreational vessels of all sizes . The second measure provided a two-year moratorium on CWA permitting for certain discharges from commercial fishing vessels of all sizes and non-recreational vessels less than 79 feet in length . This moratorium has been extended three times, most recently until December 18, 2017, which was enacted in December 2014 as part of a Coast Guard reauthorization bill. In 2008 EPA issued a national CWA permit called the Vessel General Permit (VGP), giving permit coverage to an estimated 72,000 vessels including tankers, freighters, barges, and cruise ships that were not exempted by Congress's actions. It applied to 26 types of pollutant discharge types or waste streams, including but not limited to ballast water, that result from the normal operation of covered vessels. The ballast water requirements of the 2008 VGP were minimal, largely requiring what was required by then-existing Coast Guard rules—primarily use of ballast water exchange. Like Coast Guard rules that had been in effect since 2004, EPA's permit mandated mid-ocean ballast water exchange for ships traveling outside the EEZ of the United States. Some stakeholder groups urged EPA to include numeric ballast water discharge standards in the 2008 VGP, arguing that discharge standards would encourage adoption of technology that is more effective for controlling living organisms than ballast water exchange. But EPA did not do so at the time. Requiring a numeric effluent limit for the discharge of living organisms was not practicable, achievable, or available because adequate treatment technologies were not then commercially available, EPA said. Instead, the VGP specified ballast water best management practices, such as regular cleaning of ballast tanks in mid-ocean to remove sediment, as well as recordkeeping and monitoring requirements. Because the VGP and other CWA permits are authorized for five-year periods and then must be renewed, in 2013 EPA re-issued the VGP. It is similar to the 2008 permit in many respects, but departs from the previous permit by specifying ballast water numeric discharge limits.