Ayrshire's second largest river rises above Loudoun Hill on the boundary of East Ayrshire and Lanarkshire. From there it flows for 42km westwards to Irvine Bay on the Firth of Clyde.
It shares an extensive estuary with the River Garnock. This is the only significant estuary in Ayrshire, providing excellent bird habitat.
Principal land uses in the catchment area are agriculture, forestry, and urban development, the largest settlements being Irvine, Kilmarnock, Irvine, Stewarton, Galston, Newmilns and Darvel. The river has been highly modified, particularly where it flows through urban areas, with many weirs, culverts and retaining walls. There is a large flood prevention scheme in development between Hurlford and Galston.
Fishery management is undertaken by the River Irvine Angling Improvement Association and the many active angling clubs.
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- Medium-sized river with catchment of >380km2. Second largest catchment of Ayrshire rivers.
- Rises above Loudoun Hill where it is known as the "Wee Irvine".
- Headwater's of the Craufurdland Water have been impounded for Water supply reservoirs. There is a compensation flow of 1.7Mlitres/day.
- High human population density equivalent to 295 people/km2 within the catchment.
- No major Sewage Treatment Works as all sewage is pumped to the coast for treatment.
- Water quality in many reaches of the main river and tributaries suffers from the impacts of diffuse pollution, primarily from agricultural land use. 62% of catchment land use is improved grassland.
- Major tributaries are the Glen Water, Glenoul Water, Cessnock, Fenwick and Craufurdland Water, Kilmarnock Water, Carmel Water and Annick Water.
- River is extensively urbanised where it flows through settlements of Darvel, Newmilns, Galston, Hurlford, Kilmarnock and Irvine.
- Annick Water is the largest tributary with a catchment area of 91km2.
- Irvine is recovering from is past history as an industrial river, although legacy of many weirs remain, some of which are serious obstacles to migratory fish.
- Salmon and sea trout are prevented from accessing the Fenwick and Craufurdland waters due to instream modifications at the Black Rocks Waterfall in Kilmarnock.
- Common fish species present include salmon, trout, eels, stone loach, minnows, sticklebacks, lampreys. There is a population of Gudgeon in the lower river, which is unique within Ayrshire.
- Grayling population, which were introduced in the 1850s is thought to have died out.
- There have been a number of fish kills on the Irvine in recent years with the most recent occurring in November 2006, upstream of Priestland.
- The Irvine's population of Freshwater Pearl mussels is thought to have died out.
Ayrshire Rivers Trust research and monitoring on the River Irvine includes:
- Comprehensive electrofishing surveys on behalf of the River Irvine Angling Improvement Association completed in 2003 and 2005 to investigate fish populations throughout the catchment.
- Phase One Salmonid Habitat survey of the Irvine main stem and some of the tributaries published in 2003. The survey found that good juvenile salmonid habitat was limited in the lower main stem due to low gradient and human influences such as canalisation. Habitat degradation was also an issue in some parts of the upper reaches, primarily from livestock farming. The significance of the many weirs in the catchment was also highlighted.
- Invertebrate surveying introduced in 2005 to complement other data collected at electrofishing sites.
Urbanisation in Stewarton
Dean Castle Ford across Kilmarnock Water
Culvert on Fenwick Water