The important section of the Shannon is that between Loop Head and Shannon Harbour. An occasional steamer might serve Athlone, but Lough Ree was a desert. Lough Allen coal never amounted to much, although a word must be said for the egg trade, carried by the Royal Canal to Dublin. But there is nothing up the north end to compare with the historical, cultural, political and economic significance of the lower Shannon.
The Limerick Navigation (the old pre-Ardnacrusha route)
Limerick to Athlone (including the modern route, through Ardnacrusha, from Limerick to Killaloe)
Here are the Sailing Directions for the Shannon Estuary (completed before 1848) and for Lough Erne (1835-6), Lough Ree (1837) and Lough Derg (1838-9). They were compiled by Commander James Wolfe RN, who was one of those who drew up the relevant Admiralty Charts. Like the Charts, these Directions have not been updated, so boaters should not rely on them for navigation.
The Google Books Team have kindly permitted me to extract these from a larger document, which was one of those they had scanned and placed online, and to make them available (free, of course) to visitors to this site. Note that I have omitted part of the description of the smaller Lough Derg, which is not part of the connected waterways system.