The lake lies between the Moelwyn and Nyth y Gigfran mountains above Tan y Grisiau and is fairly easily accessible on foot.It holds an abundant head of brown trout, and is a popular lake for anyone wanting to wet a line for couple of hours.
GR SH 674465.
About a half hours walk from Tanygrisiau.
Season Starts - 3rd March
Season Ends - 30th September
Fishes well with fly.
Early season, Zulu or Bibio are the flies to try, but as the season progresses, Hares Ear Nymph, Alder and Greenwells Glory come into their own.
In late May, early June, Cwmorthin has a very good hatch of "cogyn", or sepia dun.
When the fish are preoccupied on these flies, they can be frustratingly difficult to catch, but if you can "match the hatch", it can almost be a fish a cast.
As with most lakes, early morning and dusk will give the best sport, with night fishing also being very productive.