That there has been a further deterioration of the river system in Ireland since the early 1990s is the main finding of a report on water quality in the 1995-1997 period, published recently by the EPA.

This deterioration continues a trend which has been noted over the last 25 years and is attributed in the main to nutrient (phosphate) enrichment or eutrophication. While the degree of pollution is slight in many cases, it is of concern in view of its potential impact on stocks of the pollution-sensitive trout and salmon in rivers and lakes and because of the reliance on these as sources for the bulk of the public water supply. It also has implications for the attainment of the goal of good ecological quality for waters, set by the proposed EU Framework Directive on water management.

The report gives assessments of the water quality of some 13,000 km of river and stream channel, 120 lakes and 23 estuarine and coastal waters. In addition, for the first time, an overview of the quality of ground waters is given, based on sampling at nearly 200 representative locations, as well as information on the situation in the main canals. The bulk of the data presented arises from survey work carried out by the local authorities and the EPA, with additional information being supplied mainly by the Marine Institute and the Central and Regional Fisheries Boards.

The assessments of the water quality of rivers and lakes given in this report have a particular significance in relation to the Phosphorus Standards Regulations adopted in 1998. Where a river stretch or a lake has been assessed as polluted in the 1995-1997 period, the Regulations require that specified improvements be achieved by 2007, while waters classified as unpolluted must be maintained as such.

The water quality classification of the river channel length surveyed in the 1995 - 1997 period is given in figure 1. This shows that only 67 per cent was assessed as unpolluted. The highest proportions of polluted channel were recorded in the eastern and south-eastern regions and the lowest in the southern and Donegal - Sligo parts of the north western region. Figure 2 contrasts the situation for the last three periods of review, and shows an ongoing reduction in the length of unpolluted channel since 1987-1990.

Most of the slight and moderate pollution was attributed to agricultural activities while municipal waste discharges were judged to be responsible for most of the serious pollution. Although still small in overall extent (less than one per cent), the level of serious pollution showed an increase for the first time since the national surveys commenced.

The number of fish kills recorded by the Marine Institute in the period (173) showed an increase compared to the 1991-1994 (116) period. Agriculture was the cause of most (97) of the kills in 1995-1997 followed by industry (37) and sewage (24). The increase in 1995-1997 reverses a decreasing trend which had been evident since the mid-1980s.

The overall quality of canal waters and their feeder streams was judged to be good.

Of the 120 lakes surveyed in the period, 97 were assessed as unpolluted, seven slightly polluted, 11 moderately polluted and five seriously polluted. Loughs Ramor and Oughter, two of the State's larger lakes, were placed in the latter category. As most of the unpolluted lakes are small, the lake surface area so classified was only 65 per cent of the total area surveyed. Overall, there was little change in the extent of water pollution in the lakes since 1991-1994. Although the surveys in 1995-1997 covered only a small proportion of the lakes in the State, they are regarded as representative and include most of the larger lakes.

Data for the estuarine and coastal waters indicate that, with a few exceptions, these are not significantly impacted by pollution. Exceptions include the Lee estuary and inner Cork Harbour, the Castletown estuary near Dundalk and localised areas of the Liffey, Shannon and Garavogue (Sligo) estuaries which are affected by municipal discharges. Sustained eutrophication was judged to be affecting only a few areas, viz., inner Cork Harbour and the Broadmeadow estuary at Malahide. The enhanced growths of algae noted in the middle reaches of the Slaney, Barrow-Nore-Suir and Bandon estuaries may be partly due to the natural characteristics of these waters.

The generally satisfactory condition of bathing waters and the low levels of potentially toxic pollutants in commercial fish and shellfish provide further evidence of the limited impact of waste discharges in tidal waters. The new and upgraded waste treatment plants planned for the major coastal towns and cities over the next few years will further reduce the pollution threat to these waters.

The survey of ground waters in the period indicated that there is no widespread pollution of particular aquifers. However, a significant number of the sources sampled showed signs of organic pollution and nitrate contamination. Of particular concern was the presence of faecal coliforms which were detected in over 30 per cent of the samples analysed for this parameter. This contamination is likely to be a major cause of the relatively poor quality of the private water supply schemes, as described in the national drinking water reports, and emphasises the need to disinfect all groundwaters used for supply.

It is concluded that the reduction of phosphorus inputs to freshwaters remains the chief task facing the water pollution control agencies. While there have been some success stories, it is clear that the measures taken to reduce eutrophication in the inland waters over the last two decades have been too limited and that the problem remains a major challenge.

In view of this situation, new management initiatives at catchment level, e.g. for Loughs Conn, Ree, Derg and Leane and for the rivers Boyne, Liffey and Suir, together with the statutory requirements under the Phosphorus Standards Regulations, are welcome and form a systematic approach to eutrophication control. They should contribute significantly to the achievement of good quality in our rivers and lakes, an objective highly desirable in itself, but also a requirement which will arise under the proposed EU Framework Directive on water policy.

Water Pollution.

The simplest definition of water pollution is "the loss of any of the actual or potential beneficial uses of water caused by any change in its composition due to human activity". The beneficial uses of water are varied and include its use for drinking and for domestic purposes, for watering livestock and for the irrigation of crops, for fisheries - both game (salmonid) and coarse (cyprinid), for industry and for food production, for bathing and for recreational and amenity use. If water is rendered unsuitable for any of these purposes then it is polluted to a greater or a lesser degree depending on the extent of the damage caused. The inclusion of the word 'human' in the definition is necessary because water may be naturally impaired in quality either temporarily or permanently.

Natural Water

Pure water - water absolutely free from any substances dissolved in it - does not exist outside the laboratory, as natural water contains dissolved gases and salts. These substances are often the very factors which make the water suitable for particular beneficial uses.

Water must have an adequate level of dissolved oxygen if fish are to thrive - without it they will die. (As explained later, the great majority of pollution instances on our rivers are attributable to the depletion of the dissolved oxygen, leading to various highly undesirable effects.) Again drinking water without dissolved oxygen and with only a very low level of dissolved salts, is not very palatable: it is the level of salts in solution - as natural 'hardness', for example - which gives many waters their palatability.

Potential Beneficial Uses

It cannot be accepted that natural waters will be immediately suitable for the whole range of beneficial uses. Nobody should expect to be able to drink the water in any river, for instance, without its being treated before use. More importantly, river water is most unlikely to be microbiologically pure, that is, free of those minute organisms, some of which can cause diseases in humans.

In these cases, water pollution means that, because of some human activity the water is no longer suitable for some potential use, such as drinking water, even after treatment. To illustrate, if a river from which water is taken for treatment for drinking receives a discharge of chemical or possibly toxic waste, the water may be made completely unsuitable for eventual distribution. The local authority treatment works will usually have been designed to remove the natural contaminants - colouring particles, particles causing turbidity, micro organisms, etc. - and therefore may be unable to cope with a heavy load of completely foreign matter such as chemical waste.