Engineering works on the Inny River in the 1960s drained enough water from Lough Derravaragh to reveal a prehistoric landscape that had been submerged for millennia, bringing a scatter of worked stone back into the world.

The island is a knoll of calcite mudstone threaded with bands of chert, a fine-grained flint-like rock that Mesolithic people valued highly for knapping into tools and blades. Debitage flakes, the waste fragments produced when knapping chert into usable shapes, were found lying about in some quantity when Professor Frank Mitchell documented the site in 1972, designating it Site 2b in his study of the area. What made this chert particularly notable was its unusual banded structure, described as 'festoon' chert, a formation that also disintegrates readily on exposure to the weather. Research has since suggested this material may have been quarried originally from natural outcrops at Knockeyon Hill nearby, implying that people were not simply using whatever lay at hand but were selecting and transporting specific stone to this location. The combination of workable raw material, a lakeshore setting, and what appears to have been deliberate occupation makes Clonava Island an unusually legible trace of early prehistoric activity in the Irish midlands.

Nothing of the lithic scatter remains visible at the surface today. The flakes Mitchell described have since been lost to weathering, the same process that gradually destroys the banded chert itself. The site endures now mainly in the documentary record, a place where the evidence appeared briefly, was noted, and has since quietly disappeared again.