Water Quality Guidelines No.2: Colour and Clarity
Guidelines for the management of water colour and clarity.
This publication is available as PDF only.
Executive Summary
Background
Public perception of water quality is dominated by visual and aesthetic factors. Colour and clarity are specifically protected by the Resource Management Act 1991. Sections 70 and 107 specify that there shall be no "conspicuous changes in colour or visual clarity" following the discharge of contaminants. Substances which alter optical water quality may also affect aquatic life. The Act also prohibits "significant adverse effects on aquatic life". Optical quality can also affect the suitability of recreational bathing waters, and visual clarity is protected in Class CR waters.
"Conspicuous change" is not defined in law. The Courts have concluded in a different legal area that for something to be "conspicuous" it must be more than "clearly visible". While it is difficult to determine experimentally when a conspicuous change has occurred, studies have been carried out to determine the level at which a change in clarity can de detected.
