Final answer:
The Shannon River is the river that has its mouth at Limerick, Ireland. It is an important waterway that runs through the country, offering both historical significance and natural beauty.
Step-by-step explanation:
The river whose mouth is at Limerick in Ireland is the Shannon River. This significant waterway is not only noted for its picturesque setting, but it also serves as an important geographic feature for both transportation and tourism. The Shannon River runs across the length of the country and is integral to the Irish inland waterways.
Limerick, a city built on the banks of the Shannon, boasts a rich history and has been a major port for centuries. The river, indeed, provides an enchanting backdrop to historical sites and modern amenities alike. It is well-known for the scenic beauty that surrounds it, as well as the diverse wildlife that inhabits its waters and banks.