River Derreen

{{short description|River in southeastern Ireland, tributary of the Slaney}}

{{Use dmy dates|date=February 2020}}

{{Use Hiberno-English|date=February 2020}}

{{Infobox river

| name = River Derreen

| native_name ={{native name|ga|An Daoirín}}

|name_etymology = Diminutive of doire, Irish for grove, esp. oak{{Cite web|url=http://www.logainm.ie/en/116234|title = An Daoirín/Derreen River}}

|image = Disused footbridge - geograph.org.uk - 708062.jpg

| image_caption = Footbridge over the Derreen River near Hacketstown

| source1_location = Lugnaquilla, County Wicklow

| mouth_location = Tullow, County Carlow

| length_km = 40

| subdivision_type1 = Country

| subdivision_name1 = Ireland

| subdivision_type2 = Cities

| subdivision_name2 = Hacketstown, Tullow

| subdivision_type3 =

| subdivision_name3 =

| basin_size_km2 = 201.18

| discharge1_avg =

|mouth=River Slaney}}

The River Derreen ({{irish place name|An Daoirín}}) is a large river in the southeast of Ireland. It rises on the southern slopes of Lybagh and Slievemaan and flows southwest until it joins the River Slaney in County Carlow,{{cite book |last=Joyce |first=Patrick Weston |authorlink=Patrick Weston Joyce |title=The geography of the counties of Ireland |publisher=George Philip & Son |date=1883 |location=London |pages=205 |url=https://books.google.com/books?id=S9oHAAAAQAAJ&dq=lybagh&pg=PA205 }} south of Tullow, passing close to Hacketstown and Tullow, County Carlow before it joins the Slaney upstream of Aghade bridge. Running through tillage and pastureland in its lower reaches, the Derreen with its sandy, gravelly bottom is a prime salmon spawning tributary of the Slaney.

Passing through counties Wicklow and Carlow, it is the first large, major tributary of the River Slaney.

Towns on the Derreen include Hacketstown and Tullow. It is crossed mainly by old humpbacked stone bridges. It is a rural river, flowing through only 2 major towns.