In 1809 Thomas Newenham included the Cloonastra amongst the tributaries of the River Shannon. There is no obvious logic to the order in which he listed the rivers, so it is not possible to deduce its position relative to other rivers.
In 1833 Charles Wye Williams listed it amongst rivers connected with the Shannon that might be noticed; he did so again in 1835. On both occasions the other rivers are identifiable and, to some extent, navigable, which suggests that the Cloonastra is a navigable tributary of either the inland or the estuarial Shannon.
If you know where it is, or what name it now bears, please leave a Comment. My best guess so far is that it might be the Hind River, which joins Lough Ree at Clooneskert and which might have been made navigable, but I have no actual evidence. There’s a Cloonmustra townland north of Ballyleague, but the watercourses look much smaller. Rinn River? I can’t find anywhere nearby that looks like a variant of Cloonastra.