For years Thirlmere was one of the least visited lakes in the Lake District, despite having good access. The reason for this was that it was used as a water supply reservoir for Manchester from 1889 and was closed to the public.
It's now owned by North West Water and has been opened to the public.
The lake was originally two smaller lakes separated by a narrow channel and bridge at Wath (now underwater). The water company built a 104 feet high dam at the northern end of the lakes, creating a single lake and drowning the villages of Armboth and Wythburn.
The hotel mentioned in 'A vested Interest' is the Dale Head Hall Hotel - it's a real place and a nice place to stay. It lies within walking distance of one of my favourite walks in the Lake District, Helvellyn and Striding Edge