Llyn Elsi it is. Well done Yorkie.
I've forgotten the name of the church but it's opposite the train station in Dinas. Bont Newydd,Dinas and Llanwnda are very close together but I'll find out the name and let you know.
Here's another photo of the lake that would have made it easier,
PS Since posting this I've visited the google map and you can see the Church by the houses at T'yn Llan and Google lists the Church's name as St Gw?

? so perhaps you are right again

??