State of surface waters

The quality of river water across Europe has improved significantly thanks to a range of EU environmental directives since the 1970s.

However, pressures from agriculture, urbanisation, tourism and climate change suggest that guaranteeing water quality will continue to be a critical European environmental issue.

Water quality is a complicated issue underlined by the influence of various pressures and multi-cause/multi-effect relationships. A pristine, pollution-free river flowing through an unaltered landscape may be easy to spot, but the manner in which human activity has altered and degraded it may not be. Thus, assessing the extent of the damage and progress towards recovery is not an easy task.

Conventionally, water quality is defined by biological and chemical parameters. For instance, biochemical oxygen demand (BOD) and ammonium concentrations are indicators widely used to assess the amount of organic oxygen-consuming pollution in a river. However, simple statistical parameters can be misleading because the baseline natural conditions of rivers can be very different. Hence, efforts are being made to conduct wider assessments of biological and ecological health. The Water Framework Directive aims to achieve good ecological and chemical status for all water bodies in Europe by 2015.

Pollution takes many forms. Faecal contamination from sewage makes water aesthetically unpleasant and unsafe for recreational activities, such as swimming, boating or fishing. Many organic pollutants, including sewage effluent as well as farm and food-processing wastes consume oxygen, suffocating fish and other aquatic life.

Nutrients, such as nitrates and phosphates, from farm fertilisers to household detergents can 'overfertilise' the water causing the growth of large mats of algae; some of which can be toxic. When the algae die, they sink to the bottom, decompose, consume oxygen and damage ecosystems.

Pesticides and veterinary medicines from farmland and chemical contaminants, including heavy metals and some industrial chemicals, can threaten wildlife and human health. Some of these damage the hormonal systems of fish, causing feminisation. 

Sediment run-off from the land can make water muddy, blocking sunlight and, as a result, kill wildlife. Irrigation, especially when used improperly, can bring flows of salts, nutrients and other pollutants from soils into water. All these pollutants can also make the water unsuitable for abstraction for drinking water.

Ecological quality and water quality is also influenced by the physical management of rivers and the wider hydrological environment of a river basin. Canalisation, dam building, river bank management and other changes to the hydrological flow can disrupt natural habitats, such as bank side vegetation. They can also destroy pebble riffles where salmon and other fish spawn. Seasonal flow patterns that are vital to many species can also be changed, as well as the connectivity between habitats; a very important factor for the functioning of aquatic ecosystems and for the development of the different life stages of aquatic organisms. In urban agglomerations, storm water carrying contamination from streets and roofs can contribute to water pollution if discharged directly into water bodies.

The following pages describe:

• Water quality and pollution by oxygen consuming substances
• Water quality and pollution by nutrients
• Water quality and pollution by hazardous substances