According to the EPA GIS mapping they project a water flow coming from Roosky Lough and running  through the center of the mill site, then routes between the two bogs to the SE, then up to Drumard Lough. It must be a seasonal mill as both loughs are seemingly grass-bound anyway. 
https://gis.epa.ie/EPAMaps/

I can't see how a stream takes that path as from what I can see there aren't sufficient indications in the landscape to support a flow. Additionally the old train track running near to and almost across site makes it more confusing. I suspect that flow out of Roosky L is instead feedwater to the bogs. I'll map any significant flows that I see and maybe somebody with local knowledge can fill in the dots.