Water pollution can be summed up as "the loss of beneficial uses of water caused by change in its composition due to human activity". Water must have an adequate level of dissolved oxygen if fish are to thrive. Without an adequate level they will die. The amount of dissolved oxygen present in water is extremely small. There are about 9.2 milligrammes oxygen per litre of water. Even small amounts of pollution will reduce the oxygen levels and will disrupt fish life.
The majority of pollution instances in Ireland are man made. Farming can cause soil, manure slurry and silage effluent to be washed into streams and rivers. When there is an uncontrolled discharge of organic material there is an immediate abundance of food and dissolved oxygen. This means that bacteria growth begins and the population increases rapidly. This bacteria consumes oxygen thus reducing the amount of oxygen dissolved in the water. Plants cannot survive and fish cannot survive without oxygen or food.
Pollution In Lakes.
It can take a long time for a lake to recover after it has been polluted. In many lakes the material causing the pollution may be trapped permanently in the bottom sediments.
Pollution In Rivers.
The discharge of pollution to a river can have dangerous effects on the fish and flora and fauna and it may also cause severe pollution for miles downstream where it will be unlikely to kill the river. River water is constantly flowing and once the discharge has been stopped the river can begin the recovery process. The waste will be diluted by the clean water flow and will be carried downstream. The flora will recover and the fauna will recolonise and in time the fish will return.
The Solution To Pollution.
The solution to pollution problems is control. Water quality management must enforce the national and EU standards. Farmers must take precautions in agriculture; factories must be careful when depositing waste; and the public must be aware of the problems of pollution.
Water Report
The most recent report on water quality in Ireland was published in 1996. The report was based on data collected over the period of 1991 - 1994 in relation to 13,200km of water channel.The report can be summed up as :
71.2% - Unpolluted
16.8% - Slightly Polluted
11.4% - Moderately Polluted
0.6% - Seriously Polluted
In the Western region where Claremorris is situated 1791 km of water channel was surveyed. Of that, 79.8% was unpolluted, 13.7% was slightly polluted, 6.4% was moderately polluted and 0.2% was seriously polluted.
Fish Kills
In 1997 the number of fish kills recorded reached its 3rd lowest levels since 1983. The total for the year was 42. The important factor in the improved situation was the reduction in the number of leakages from silage. Fish kills caused by untreated sewage and industrial effluents have also reduced.
The effect of discharge of effluent depends on several factors. In wet weather stream flows are high therefore damage will be low because the effluent is diluted quickly. A spillage beside a small river will lead to a much more extensive fish kill than the same quantity of effluent will cause in a larger one.
Agriculture, enrichment and industry were the most frequent causes of fish kills. Farm effluents are still a major source of fish kills but they were responsible for less than half the incidents in 1997. Enrichment is the result of leaching from an excessive use of phosphate fertiliser on land. Inadequately treated sewage has continued to cause fish kills. Discharge from swimming pools causes almost perennial problems - the water looks clean but contains levels of chlorine which is lethal to fish.
