Chairman Alan Virtue said that the main contributors were an increase in pollution from silage and slurry, and a "dramatic" rise in sheep dip incidents. Both were exacerbated by wet weather.
Seventeen dip-related incidents were recorded in 2000, compared with only one the previous year. The group estimates that tens of kilometres of watercourses were affected.
Wet weather during the autumn increased run-off. A ban on organophosphates also meant increased use of synthetic pyrethroid dips which are ten times as toxic to aquatic invertebrates.