Article 20
Protection and preservation of ecosystems
Watercourse States shall, individually and, where appropriate, jointly, protect and preserve the
ecosystems of international watercourses.
Article 21
Prevention, reduction and control of pollution
1.For the purpose of this article, “pollution of an international watercourse” means any
detrimental alteration in the composition or quality of the waters of an international watercourse which
results directly or indirectly from human conduct.
2.Watercourse States shall, individually and, where appropriate, jointly, prevent, reduce and
control the pollution of an international watercourse that may cause significant harm to other
watercourse States or to their environment, including harm to human health or safety, to the use of the
waters for any beneficial purpose or to the living resources of the watercourse. Watercourse States shall
take steps to harmonize their policies in this connection.
3.Watercourse States shall, at the request of any of them, consult with a view to arriving at
mutually agreeable measures and methods to prevent, reduce and control pollution of an international
watercourse, such as:
(a) Setting joint water quality objectives and criteria;
(b) Establishing techniques and practices to address pollution from point and non -point sources;
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(c) Establishing lists of substances the introduction of which into the waters of an international
watercourse is to be prohibited, limited, investigated or monitored.