Experience has been similar in Ireland and Norway where salmon farming has also become an important rural industry. Salmon farms directly cause problems in three main areas. First, wild salmon and sea trout are likely to suffer from the same diseases as caged fish. The risk of disease is increased by the accumulation of surplus food and feces on the seabed below sea cages in salmon farms. Second, wild sea trout have been found to be badly affected by sea lice.
Sea lice are parasites which have posed a devastating threat to farmed salmon stocks.
Third, wild sea trout are likely to be affected by algal blooms which have resulted from excess nutrients in salmon farm effluent. Further damage to wild stocks is caused by chemical treatments given by salmon farmers to caged stocks of farmed fish to protect them from disease and sea lice infestation. Some of these chemicals are highly toxic. For example, the chemical dichlorvos has been used in very large quantities. Dichlorvos is regarded as one of the most toxic chemicals which are known.