Many methods are available for the treatment of industrial wastewaters. The pollutant concentrations from aquaculture facilities are often low, but occur in high flow rates. Consequently, much care must be taken to transfer suitable technology. Of the four main types of treatment unit processes, i.e. biological, chemical, mechanical and gravitational, the latter two types are most commonly employed in flow-through aquaculture facilities in Europe. This paper identifies the properties of the wastewater upon which the units operate, the efficiency of selected examples and their suitability for various applications. Relevant strategies are recommended. A combination of screening to remove suspended particles, followed by sedimentation to thicken the resulting sludge appears, at resent, to be the most appropriate primary treatment strategy for flow-through facilities. Various other secondary or even tertiary techniques can be employed to further treat tie main effluent. These can, however, prove prohibitively expensive in high flow situations and can produce negligible improvements in environmental protection.