Conservationist Nick Jouault said that he had seen two French craft landing at the Ecréhous this week.
Mr Jouault said he felt it was very unlikely that either boat had previously been to Jersey to take the tests required for anyone arriving in Jersey.
‘One boat landed on the beach and people were swimming, and a couple disembarked from the other boat and were walking around,’ he said.
As he works in healthcare, Mr Jouault said he had not approached the French visitors and opted to keep his distance.
‘I come out here for a bit of space but I end up having to be careful,’ he added.
Andrew Hunt, of Customs and Immigration, said officers would continue to patrol the area.
‘We have been out there a number of times and French vessels seem to generally be complying with the requirement not to land,’ he said.
‘There have been a small number of incidents where there have been attempts to land and people from Jersey have spoken to them.’
Mr Hunt said he felt there was a greater awareness of Jersey’s restrictions as a result of the publicity circulated to harbour towns in Brittany and Normandy by Ports of Jersey.
Asked if there was any more that Jersey could do, Mr Jouault said he thought it would be good to have cameras sited on the reef to enable activity to be monitored.