The difficulty was that some moved on rather quickly from the scene and if in a campervan, as this trio was, were hard to trace.

"I have spoken to the campervan company involved about putting angling information, including the need for a licence, into their on-board literature, which they are looking at."

The company helped trace the Swiss men after it was explained rangers had the ability to seize vehicles, not just boats and fishing gear, Mr Hadland said.

While the two incidents were disappointing, it was also a great result so far this summer, given the high numbers of anglers out on the water. Rangers had checked more than 150 licences in the Upper Clutha lakes, he said.

"This season has been a massive one for anglers throughout the region, with great fishing conditions, in particular at the popular Central Otago lakes."