612 lakes in Northern Ireland between 1 and 100 hectares surface area were sampled in the summers of 1988-1990 . Water analyses for major ions and nutrients are presented in summary form and demonstrate the wide range of lake chemistry in the region. Altitude was the main determinant of water chemistry, which varied from near rain water to greater than 100 mg Ca 1 -1 faithfully reflecting the underlying geology, even in regions of diverse geology . `Rainfall' lakes were commonly depleted of potassium but enriched in calcium and bicarbonate compared to average rainfall composition in the area . Major ion chemistry in general plotted as expected on a diagram of Na/(Na + Ca) ratio against total dissolved solids, with major deviations only found in lakes on an offshore island or which were known to be polluted .Nutrient enrichment was widespread, 27% of lakes contained more than 100 pg TP 1 -1 enriched lakes were commonest in lowland areas but also occurred in upland lakes with afforested catchments .

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SUMMARY 1. Precipitation inputs and outflow stream outputs are presented for 1993 in an upland lake and catchment system on the Antrim Plateau, Northern Ireland. 2. Phosphorus, potassium, chloride and possibly sulphate behaved conservatively inputs were approximately balanced by outputs. Combined nitrogen outputs were very much less than inputs, whereas there was a net export of calcium, magnesium, sodium and silica from the catchment. 3. Precipitation phosphorus inputs (22 kg P km−2yr−1) are compared with literature data and are shown to be near the median value. 4. The phosphorus budget is discussed in relation to the fact that there are few oligotrophic lakes in Northern Ireland. It is suggested this is due to the rainfall inputs, low phosphorus retention by the catchment and rapid flushing rates in the lakes.

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