effects that rise to the level of “appreciable harm” are provided in paragraph 2.The definition requires only that there be a detrimental alteration in the “composition or quality” of the water. The trjrm “composition” refers to all substances contained in the water, including solutes, as well as suspended particulate matter and other insoluble substances. The term “qua1 i ty” is commonly used in relation to pollution, especialiy in such expressions as “air quality” and “water quality”. While it is difficult, and perhaps undesirable, to define the term precisely, it refers generally to the essential nature and degree of purity of water. Fourth, the definition does not refer to the means by which pollution is caused, such as by the “introduction” of substances, energy, etc., into a watercourse. It requires only that the “detrimental alteration” result from “human conduct”. The latter expression is understood to include both acts and omissions, and was thus considered preferable to such terms as “activities”. Finally, the definition does not include “biological” alterations. While there is no doubt that the introduction into a watercourse of alien or new species of flora and fauna may have hurmful effects upon the quality of the water, the introduction of such living organisms is not generally regarded as “pollution”, per 66. biological alterations are therefore the subject of a separate article, infine article 24. (3) mh sets forth the general obligation of watercourse States to “prevent, reduce and control pollution of an international watercourse [system] that may cause appreciable harm to other watercourse States or to - 160 -their environment . . .I’. This paragraph is a specific application of the general obligation contained in article 8 not to cause appreciable harm to other watercourse States, The various elements of paragraph 2 are dealt with in the following paragraphs of the commentary.
**Analysis**
This text appears to be discussing the concept of pollution and its impact on international watercourses. The definition of pollution is provided, which requires a detrimental alteration in the composition or quality of the water, resulting from human conduct. The text also mentions the general obligation of watercourse States to prevent, reduce, and control pollution. Given the focus on environmental protection and the impact of human activities on water quality, it is likely that this text falls under the category of natural resources and environment.

**Category**
Natural resources and environment, Environment