From Whittled Away:
Bred at Lough Funshinagh, County Roscommon, until 1957.
This 2015 Irish Examiner piece gives more of the story:
The species once had a special relationship with Ireland; a County Roscommon turlough held Europe’s largest breeding colony of these birds until the march of progress, in the newly created Irish Free State, destroyed it.
What a tragedy the famous colony is gone; the black-necked grebe was one of our most glamorous birds.
A hundred years ago, the black-necked grebe began a brief, but intense, love affair with Ireland.
There had been only 21 sightings of the bird here during the 19th Century and nesting had never been recorded.
In 1906, a pair tried to breed at Keel Lake, Achill.
Parents with three downy young were seen at Briarsfield turlough, County Roscommon, in 1915. Soon, grebes were breeding at several locations in the west.
In 1929, nests were discovered at Lough Funshinagh, a County Roscommon turlough. By 1932, there were 300 pairs there.
The black-necked grebe is a rather temperamental creature, apt to change its breeding location if everything isn’t entirely to its liking.
Turloughs, with their notorious habit of disappearing down a swallow hole from time to time, seem unlikely places for such pernickety birds to nest.
‘Nature was in the mood for magic in County Roscommon on Monday when, sharp at 12 noon, Lough Funshinagh, with a farewell roar, completely disappeared’ declared the Westmeath Independent in 1955. On November 22 of that year ‘swans geese, and thousands of fish, suddenly found themselves without any water’.
The departure of the grebes from Funshinagh, however, is usually blamed on local drainage measures and on the development of the Shannon hydroelectric scheme which affected the water table from 1934 onwards.
The Briarsfield turlough, which had up to 15 nesting pairs, was drained in 1957.