Unless emergency action is taken, there will be a repeat of the scenes last winter when up to 1,000 salmon died on the River Nore at Kilkenny city.
Adult fish returning to spawn have been turning up on the banks of the Nore, having failed to mount a fish pass built using incorrect water levels which was supposed to ensure safe passage for them.
Anglers have been gathering at Lacken Weir, off Maudlin Street, to watch the fish attempting to scale the faulty pass.
There had been earlier assurances from the Office of Public Works (OPW) that there would be no repeat of last year's scenes of fish perishing after failing to get over the pass, which was altered in the summer of 2004 as part of the Nore flood relief scheme. In September of this year, the OPW admitted there were "construction defects in the new section of the weir".
Southern Fisheries Board manager Brian Sheerin said the board will meet with Department of the Marine engineers on site today to discuss emergency measures.
The situation has been exacerbated by the "upgrade" of a second smaller fish pass on the weir by the OPW which is not working either. Kilkenny Anglers' Association chairman Tommy Hoyne said salmon were jumping on to the smaller fish pass but were being forced back by the current on to the rocks excavated during the upgrade and left there.