Water Quality Issues

The Dee is regarded as one of the least contaminated of the larger Scottish rivers. This is mainly because the Dee has not suffered from the impacts of industrial pollution, since there is no heavy industry in the catchment, and because the river is not navigable, except in its estuary. However, although the River Dee itself is largely of excellent quality, impacted areas and downgraded tributaries do exist. In particular, in the lower half of the catchment, contaminants entering the catchment’s water courses from diffuse sources, such as agricultural, forestry and urban runoff, are having a major impact collectively. In addition, although point source pollution is no longer the problem it was in inland waters (due to the successful implementation of the Control of Pollution Act), sewage effluent is still a major pollutant.

Diffuse water pollution is mainly related to the way we use and manage land and soil. It can affect rivers, lakes, coastal waters and groundwaters. Groundwaters are affected by leaching of pollutants from the land surface and from areas of contaminated land; where the groundwater connection with surface waters is high, pollution can pass from one to affect the other. Surface waters are greatly affected by rainfall that washes over and off the land (run-off). Run-off has increased as agriculture has intensified and as we have built more roads and houses, particularly where we have degraded the natural permeability of the landscape and reduced its capacity to retain and filter water.

Diffuse pollution results from release of a variety of substances in many different situations. Sources of diffuse pollution in the Dee catchment include:

  • nutrients such as nitrogen and phosphorus from over-application of fertilisers and manures;
  • faecal and other pathogens from livestock and from overloaded and badly connected drainage systems;
  • soil particles from arable and livestock farming, upland erosion, forestry, urban areas and construction and demolition sites;
  • pesticides, veterinary medicines and biocides from industrial, municipal and agricultural use, poor storage and handling, and run-off;
  • organic wastes (slurries, silage liquor, surplus crops, sewage sludge and industrial wastes) that are poorly stored or disposed of and spread to land;
  • oil and hydrocarbons from car maintenance, disposal of waste oils, spills from storage and handling, road and industrial run-off;
  • chlorinated solvents from industrial areas where the use of solvents is ubiquitous;
  • metals, including iron, acidifying pollutants and chemicals from atmospheric deposition, abandoned mines, industrial processes etc.

Diffuse water pollution can have significant effects on wildlife and our use of water. These effects include:

  • groundwater and surface water contamination and the subsequent loss, or need for treatment, of drinking water resources;
  • microbiological contamination of water supplies;
  • smothering of fish spawning gravels;
  • nutrient enrichment and eutrophication;
  • oxygen depletion;
  • toxicity to plant and animal life, including endocrine disruption in fish.

Unlike point source pollution, we cannot easily control diffuse pollution by issuing licences or permits. Regulatory approaches have to be more subtle and in many cases need to be well connected to the land use planning system. The Dee catchment’s water quality can only be improved by addressing diffuse pollution issues and by adopting innovative ways of controlling the risks from diffuse sources. The Water Framework Directive may offer fresh opportunities for this.

The blue Action Cards (numbers 1-14) in Part 2 of the CMP address 14 Water Quality Issues.