There is no uniform approach to the designation of zones to accommodate liquid waste discharges into an aquatic receiving system without interference with other beneficial uses. This leads to confusion and in-decision among dischargers and enforcement agencies. Acceptance of universally adaptable guidelines would initiate understanding and progress. Such conceptual guidelines are proposed, including: initial establishment of the waste capacity of the receiving system; control of mass emission rate of critical materials; adoption of aesthetic criteria; establishment of water quality requirements in the mixing zone based on time exposure history; derivation of specialized criteria to permit overlapping mixing zones; limiting the total region of a waterbody devoted to mixing zones; assessment of damage to biota on a population basis; recognition that limited loss of living area may not be significant to populations; early acknowledgment that siting and discharge design can afford protection to uses; and that a case-by-case approach is essential to wise use of natural resources.