The father and his young son tragically fell into a stream beside the Royal Canal in Dublin after visiting relatives.
The man, named locally as Sean 'Curly' Sweeney (36), had been visiting a relative on Easter Sunday with his three-year-old son Tyler Joyce when the tragedy occurred.
It is believed the pair fell into the water accidentally, as they took a short-cut home.
The bodies of the father and son were discovered by a passer-by, who immediately alerted emergency services.
Despite the best efforts of paramedics, they were pronounced dead at the scene.
The shocking incident came to light at about 3pm yesterday in the Ashington Park area of Ashtown, Co Dublin. However, it is not know how long the pair were in the water.
A post-mortem is currently taking place at the Dublin City morgue in Marino. The results will be known later this evening but are unlikely to be published.
A senior source said they are expected to confirm that the deaths were a result of a tragic accident.
The results of the post-mortem will guide the direction of the investigation.
Gardaí sealed off the scene yesterday as senior detectives arrived to carry out investigations into the tragedy.
Gardaí were also in the process of interviewing relatives in the hopes of piecing together the exact circumstances which led to the deaths.
As the child's mother Pamela Joyce was comforted by relatives, shocked locals gathered at the scene yesterday. They looked on in disbelief as an ambulance arrived shortly before 6pm to remove the bodies. One local man described the incident as "truly horrific", adding that he knew the dead man.
"I would have known him to see around, his family live near to where it happened. The two of them were on their way to the father's house," the local man said.
As the family of the victims gathered at Mr Sweeney's home, one grief-stricken young man, believed to be related to the child, had to be restrained by gardaí.
Despite the investigation being in the preliminary stages last night, gardaí were not treating the deaths as suspicious. They believe it was simply a tragic accident.
The Garda Water Unit were in the area today searching the waters where the pair were discovered. The officers were seen using a ladder to descend to the location.
Local Labour councillor Brendan Carr said the community has been left "devastated" by the news.
"Naturally, our hearts go out to the families involved in this incident. It is the second tragedy involving a child to occur in this body of water in recent years.
"It must now be a necessity to implement safety procedures and standards in this area," he said.
The politician said the pair were in the area visiting a relative for Easter Sunday.
Mr Carr said: "This man was originally from Finglas. He was a very nice young lad. He was bringing the child over to a relative to get some Easter eggs.
"He lived in Finglas and this was a short-cut home. This is horrific, God help them."
North Dublin TD Noel Rock said: "This is an unspeakably tragic incident. Easter is always a time for family, so to hear of someone passing away tragically on their way home is truly sad. My heart goes out to the family, and to those affected by this awful loss."
A spokesman for Irish Rail confirmed that trains between Ashtown and Broombridge stations were stopped for 30 minutes after the discovery.
"At the start, it was unclear if this was on rail or canal so we had to stop the train.
"It was stopped for around half-an-hour.
"There were a couple of hundred passengers on the trains at the time but when they learned the circumstances they weren't too upset about the delay," he said.