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Water quality results

Scotland has an extensive network of rivers and streams. They have substantial biodiversity, conservation and economic value, and SEPA aims to protect and, where appropriate, improve their quality. In order that progress is made in this task, SEPA has built up an extensive monitoring network designed to represent the quality of all significant waters. Thus, river lengths are assigned the quality of a downstream monitoring point. For the purposes of river length measurement, the smallest streams with catchments less then 10 km2 have been excluded, except where they are the main source of a larger river, or they are substantially polluted. This is in accordance with European conventions, and avoids having to monitor small streams which may seasonally dry up. The total length of rivers with a catchment area of 10 km2 or more is 24,404km and SEPA's efforts are focused here. In 2003, about 800km of these rivers were considered to be of poor quality or seriously polluted, with a further 2,400km of only 'fair' quality.

• Water Quality Classification 2006  (95k)
• Water Quality Classification 2005  (176k)
• Water Quality Classification 2004  (103k)
• Water Quality Classification 2003  (78k)
• Water Quality Classification 2002  (83k)
• Water Quality Classification 2001 (70k)
• River Classifications 1996-2000
• Estuarine Classification 1996-2000
• Coastal Classification 1996-2000
• Estuarine and Coastal Classification Scheme  (70k)
• Water Quality Classification - Interactive Map

The classification network

In 1974 a river quality classification scheme was developed to monitor the quality of all rivers in Scotland. Since the formation of SEPA in 1996 the scheme was has been enhanced to incorporate developments in technology and science. The scheme is based on a five point scale and includes all rivers with a catchment area of 10 km2 or more and specific smaller rivers where known pollution problems exist. This is called the "classification network".

The classification network is divided into river stretches at confluences and pollution pressures. Every stretch is assigned a monitoring point where chemical and/or ecological surveys are taken and the aesthetic appearance recorded. The quality or "class" of a length of river is calculated from the monitoring point results. The stretch lengths in each class are added together.

Unclassified river stretches are mostly located in rural upland catchments. It is SEPA's intention that the extent of unclassified rivers will be progressively reduced to near zero by the time EU Water Framework Directive systems are in place in 2006. This process has been underway for a few years, and in 2003 the length of unclassified rivers was reduced by a further 2752km.

How is the quality of a river determined?

Every stretch is assigned a monitoring point where chemical and/or ecological surveys are taken and the aesthetic appearance recorded chemistry results are used where a minimum of 12 samples is available from the preceding three year period, except in a very few cases where a significant change in quality occurs in a year (eg closure of a significant discharge). In this case, a minimum of 12 samples within a single year since the change are required. The standard chemical quality sampling frequency is six or 12 samples per year, dependent on the type of site. The ecological assessment is based on data collected from at least two surveys of invertebrate fauna each year. In some areas where water quality is "excellent" ecology data is collected once in every three years unless a problem in water quality is detected. If any problem is detected in normally clean rivers, this results in immediate investigation and improvement action and restoration of more frequent ecology sampling, until water quality is shown to have been restored.

Aesthetic conditions are based on one year's data from a minimum of three observations of the extent of litter and solid waste impact in the river assessed and recorded during ecological and/or chemical sampling visits

The final allocation of the quality class is based on the lowest class determined from the chemistry, ecology, aesthetic and toxicity assessments for the associated monitoring point. No attempt is made to assign zones of intermediate quality between stretches differing by more than one class.

The samples on which classification is based are those from the SEPA's planned routine monitoring programme, whether they are of normal quality or impacted by a short-term event. Data resulting from any additional investigative sampling in response to pollution incidents or complaints are not used.