The river catchment around Wicklow Town includes the area drained by the Rivers Avoca and Vartry.  The bedrock underlying the Wicklow Mountains is granite while slates and quartzites underlie the eastern coastal part of the catchment. 

The Vartry River rises on the eastern slopes of Djouce Mountain, flowing south and through the Upper and Lower Vartry Reservoirs. The river then enters the steep-sided Devil’s Glen, through the eastern Wicklow hills and into the northern end of Broad Lough, from where it flows into the sea at Wicklow Harbour. The hilly coastal area of Wicklow between Wicklow town and Arklow is drained by a series of south easterly flowing rivers including the Three Mile water, Potter’s and Redcross Rivers. The Avoca River system drains most of the Wicklow Mountain area. The Avonmore River rises to the south of the Sally Gap, flowing through Lough Tay and then Lough Dan, continuing south where it is met at Laragh by the Glenmacnass, Glendasan and Glenealo Rivers.

The Turlough Hill pumped storage hydroelectric generating station is situated on the headwaters of the Glendassan River. The Avonmore continues south through Rathdrum to the Meeting of the Waters where the Avonbeg River joins. Now called the Avoca River, it continues past its namesake town to Woodenbridge where the Aughrim River flows in. This tributary is the combined outflow from the Ow River and the Darry Water. Downstream of Woodenbridge, the Avoca River flows through a flat-floored, steeply-sided valley before becoming tidal just upstream of Arklow Town, through which it flows before it makes it way to the sea via Arklow Harbour.

According to the Environmental Protection Agency (EPA), in County Wicklow, there are 34 rivers and four which are in very good condition, however, twenty-eight rivers and the Upper Glendalough lake in the catchment that are ‘At Risk’ of not meeting their water quality objectives. Broad Lough, which is the wet-land adjacent to Wicklow Town and Avoca Estuary are endanger of not meeting required water quality standards and action will have to be taken to improve the water quality.

By Stefan, Gary, Evan, Luke, Aaron and Michael