(4) In applying the general obligation of article 8 to the r%se of pollutlon, the Commission took into account the practical consideration that some international watercourse[s] [systems] are already polluted to varying degrees, while others are not. In light of this state of affairs, it employed the formula, “prevent, reduce and control” in relation to the pollution of international watercourse[s] [systems]. This expression is utilised in the 1982 United Nations Convention on the Law of the in connection with marine pollution, m/ with respect to which the situation is similar. The obligation to “prevent” relates to new pollution of international s] [ syetems] , while the obligations to and “control” relate to existing pollution. steps are necessary to prevent new pollution from existing or planned activities, such as factories, disposal systems, or projects, to the extent that such pollution “may cause appreciable harm to ’ other watercourse States or to their environment”, As with the obligation to “protect” ecosystems under article 22, the obligation to “prevent . . . pollution . . . that may cause appreciable harm” includes the duty to prevent the threat of such harm. This obligation is signified by the words “may cause”. Furthermore, as in the case of article 22, the principle of especially in respect of dongtirous substances such as those that are toxic, persistent or bioaccumulative. J,.W The requirel,lent that watercourse States “reduce and control” existing u.wUnited Nations Convention on the Law of the Sea, article 194, pare, 1. J&u/ See paragrtph (3) of the commentary to article 22. Jls!z/ Ese the commentary to article 22, especially paragraph (3), note 151 and accompanying text, and paragraph (9), note 176 and accompanying text, - 161pollution reflects the practice of States, in particular those in whose territories polluted watercourses are situated. This practice indicates a
**Analysis**
The text appears to be discussing the obligation of states to prevent, reduce, and control pollution in international watercourses, highlighting the importance of protecting the environment and ecosystems. This suggests that the text is related to environmental issues and the management of natural resources.

**Category**
Natural resources and environment