UK ECN site. The River Eden drains some 400 km2 of north Fife, 307 sq. kms of which lie upstream of the ECN site at Kemback. The river rises at around 220 m.o.d. and the catchment is predominantly low-lying. The major land use in the area is arable farming and approximately 76% of the catchment is prime agricultural land with very fertile soils or imperfectly drained brown forest and alluvial types. Underlying geology comprises Devonian and Carboniferous strata, the former including the most productive aquifer in Scotland, the Knox Pulpit formation. Water is abstracted from groundwater, the river and its tributaries for irrigating crops. The Balmalcolm area of the catchment is a designated Nitrate Vulnerable Zone under the EEC Nitrate Directive. Although treated sewage is discharged to the river from several small communities and from the town of Cupar, the effect of diffuse inputs from agriculture is believed to be critical to river water quality. There is a modest salmon run to the river and otters are present. The river enters the sea 4 km to the north of St Andrews and its estuary forms the Eden Estuary Local Nature Reserve - an important overwintering site for wildfowl and waders.