Athlone Sub-Aqua Unit received a call last evening.
Gardaí are appealing for information after a person was reported entering the River Shannon in Athlone yesterday.
Athlone Sub-Aqua Search and Rescue Unit received a call at around 8 o'clock last night, after the sighting at the Strand.
The Malin Head Coast Guard along with the RNLI Lough Ree Life boat and Irish Coast Guard Helicopter Rescue 118 from Sligo were also involved in the operation.
The Garda Sub-Aqua Unit are also involved in the search.
The combined search continued for a number of hours last night and is resuming this morning.
PR officer for the Athlone Sub Aqua club Cormac Nott explains how the search will be co-ordinated today:
Anyone who was in the area around 7.45 or 8 o'clock yesterday evening is asked to contact Athlone Garda Station on 09064 98550.