United States requires the use of this technique for ships destined for the Great Lakes and upper Hudson River. Continuous flushing of ballast tanks is thought to be an acceptable alternative technique for changing ballast water at sea. However, neither of the options for changing ballast water is suitable for all ships or all trade routes under all circumstances.

Conclusion 3. A ballast water operations plan, developed in conjunction with the ship cargo plan for each voyage, would provide flexibility in managing ballast water. Such a plan would take account of available information on locations and times when ballast is likely to contain unwanted organisms.

Conclusion 4. The member states of IMO are currently drafting a proposed new annex to MARPOL 73/78. Essentially, this annex would make mandatory the use of the existing voluntary guidelines. A new annex to MARPOL 73/78 probably would not be in force before the turn of the century. In the meantime, some countries already are establishing unilateral regulations for the control of ballast water introductions. Such unilateral controls could have significant negative consequences for ships in worldwide trade.

Conclusion 5. Developing regulations to control ballast water operations will be most effective at the international level. Without a governing international framework, and considering the diversity of vessels, trade routes, and ecosystems, controls tailored to local circumstances could lead to a patchwork of national (and state) regulations and resulting difficulties in compliance. The scientific and technical basis for ballast water regulations needs to be updated continuously to take advantage of R&D in the United States and other countries that leads to a better understanding of the problem of aquatic nuisance species and improved technologies for controlling ballast water.

Conclusion 6. Early involvement of all interested parties is important to the successful development and implementation of guidelines and regulations for the control of ballast water. The problem of nonindigenous species transfer has implications for society as a whole and is not simply an issue for the shipping industry.

Conclusion 7. Onboard systems for treating ballast water would give ships the most flexibility for managing ballast water, although port-based systems may offer some advantages. Experience with land-based waste water treatment systems is a useful starting point for assessing candidate technologies for treating ballast water on board ships. However, the operational constraints associated with shipboard use, including the high flow rates associated with pumping ballast water and the presence of sediment, impose additional demands on candidate systems.

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