My fishing club (Gilford Angling Club) owns Kernan Lough in the drumlins between Gilford and Banbridge. The old boys often talked about a group of people drowning in the Lough in bygone years, it often has an eerie feeling when you are fishing into the dark on your own on the far tree lined bank.
A quick trawl uncovers :
TULLYLISH, a parish, in the barony of LOWER IVEAGH, county of DOWN, and province of ULSTER; containing, with the post-town of Gilford (which is separately described,) 10,501 inhabitants. The parish formerly was part of the property of the powerful family of Maginnis, Lords of Iveagh; it was forfeited in consequence of the part taken by the head of the family in 1641. At the commencement of the war which broke out in that year, a body of Protestant women who were sent by Sir Phelim O'Nial from Armagh to Claneboy, were forced to cross Lough Kernan, in this parish, during a severe frost, when the ice having given way when they were in the middle of it, the whole party perished
http://radiocarbon.pa.qub.ac.uk/local/townlands/Down/T/tullylish.html
The BBC has a rather interesting piece relating to the Secrets of Kernan Lough:
"And further sayth, that about the beginning of March, 1641 about four score men, women, and children of English and Scottish were sent by direction of Sir Phelim O'Neile from the County of Armagh downe to Claneboys, in the County of Downe where they were met by one Capt. Phelim M' Art M'Brian, and his company of Rebells (most of his owne Sept), which said CaptaiI Phelim and his company carried and forced all these protestants from tkence into a lough called Lough Kearnan in the same county In which Lough, he and his said company forced (them upon the ice) and drowned them all, both men, women, and children, spareing none of them at all."
http://www.bbc.co.uk/legacies/myths_legends/northern_ireland/ni_6/index.shtml