Shannon River Basin a measurement of . When added to the Shannon's estuary this gives a total river flow of , which makes it the longest river within the River Shannon basin (from source to mouth)— longer than the Shannon Pot source. Thus the Boyle-Shannon river can be regarded as having the longest natural river flow in Ireland. The River Shannon Basin touches more than half (17) of Ireland's counties:- Limerick, Clare, Tipperary, Offaly, Westmeath, Longford, Roscommon, Kerry, Galway, Leitrim, Cavan, Sligo, Mayo, Cork, Laois, Meath and Fermanagh. There are many towns situated in the Shannon Basin. Towns and Villages (with 2011 populations)
County Cavan springs near Bailieborough; the River Annalee which flows from Lough Sillan and joins the Erne; and the Cladagh river which rises from Cuilcagh and flows into Fermanagh. The Glyde and the Owenroe also source in Cavan. Cavan is known as 'The Lakeland County' and is reputed to contain 365 lakes. At , Lough Sheelin is the county's largest lake; it is situated in the south of the county and forms a three way border on its waters between counties Meath, Westmeath and Cavan. A large complex of lakes form in the north and west of Cavan into designated Specially Protected