Which river is the longest in Ireland?

The Shannon River is the longest river in Ireland, stretching approximately 360 kilometers (224 miles). It flows from its source at Lough Allen in County Leitrim southward to the Atlantic Ocean, where it empties at Limerick. The Shannon is not only significant for its length but also for its historical importance and its role in Irish culture and economy. It is often associated with activities such as fishing, sailing, and tourism, adding to its prominence as a geographical feature in Ireland.

The other rivers listed, such as the Seine in France, the Tagus in Spain and Portugal, and the Rhône in Switzerland and France, are significant rivers in their own right but do not have any geographic connection to Ireland, nor do they hold the title of the longest river in that country. Thus, the Shannon stands out as the correct answer for this question regarding Ireland's geography.