The 2016 National Swimming Championship, which also double as an Olympic qualifying meeting, are underway at the National Aquatic Centre in Dublin.
The event represents the last opportunity to qualify for the European Championships which take place in London in May.
Fiona Doyle, Shane Ryan and Nicholas Quinn have already booked their place in Rio this summer after beating the qualification times for the Olympic Games, while 13 Irish swimmers and three divers have qualified for the European Championships.
The 16-year-old Conor Ferguson and UCD student Alex Murphy are both just marginally off the FINA A Olympic Qualification time in the 100m Backstroke and 100m Breaststroke respectively and will hope to dip below the required times this week.
Ferguson and Murphy will also be part of an Ireland 4 x100m Medley Relay team along with Jordan Sloan and Brendan Hyland on Saturday as they look to post a time that would see Ireland send a relay squad to the Olympics for the first time ever.
The finals on day one are off the block at 5.30pm.