Fishermen have filled the hole with rocks to reduce risk of injury.
Users of the popular pier reported the hole, roughly half a metre wide, to both the Vale and St Sampson’s douzaines, who contacted relevant States of Guernsey departments.
Vale junior constable Bill Cohu said there were holes in all of the northern piers.
‘On the other side of the bay Les Amarreurs is suffering the same problems,’ Mr Cohu said.
He thinks that repairs should be done before the summer holidays bring scores of children to visit Rousse.
‘We all know the money in the States coffers isn’t enough to chuck around, but this could be a quick job. It’s not such a big hole, but it will become a big problem if it isn’t fixed soon. A guy with a bucket and cement mixer could do it in a few hours.’
Swimmer June Richards said: ‘This slipway is falling apart – it needs repairing, it’s very dangerous. People of all ages come here and it’s a working pier.
‘We’ve all been complaining. I use a walking stick and, the trouble is, this has been going on for a long time.’
Repair work has not been up to scratch so far, she said.
‘They came and put a patch of ‘concrete on a year or so ago, but they don’t do a proper job.
‘There’s all that going on with the harbour [development plans in Town] but they don’t sort out what really needs doing.’
Agriculture, Countryside & Land Management Services have told the parish that repairs will be carried out and it is working with contractors to decide how best to do it.