Five people died after their SUV slipped off the pier
It is the first anniversary of the Buncrana Pier tragedy, in which five people lost their lives.
The jeep they were travelling in slipped on algae and plunged in to the water.
There were six people in the SUV when it went off the pier on the Inishowen Peninsula.
A young baby survived the tragedy, after Davitt Walsh - a member of the public - jumped in to save her.
When Davitt reached the car Sean McGrotty (49) told him to "save the baby", Rioghnach-Ann McGrotty.
Within seconds the car was submerged. Rioghnach lost her father Sean, her brothers Mark (12) and Evan (8), her grandmother Ruth Daniels (57), and her aunt Jodie-Lee (14).
A memorial mass will take place later at Holy family Church in Ballymagroarty, where the five victims were buried last year.
Fr Joe Gormley has been in close contact with Louise James - who lost her partner, two sons, mother and sister.
"Grief is for all of us, public for a while, we go back into our privacy.
"But on a tragedy of this scale it is always going to be the public nature of it.
"And it's that whole difficulty of trying to grieve with that sort of public spotlight, which inevitably comes in a situation like this.
"But it is very difficult".