Visitors to the Waitaki district are being told they risk losing access to the local lakes if they continue polluting the water.
The regional council Environment Canterbury, along side the Upper Waitaki Water Zone Committee, launched a campaign saying 'one poo can close the lake'.
Committee chair Simon Cameron said it will be even more important that everyone does their bit to protect water quality this summer, as Covid-19 international travel restrictions are set to boost lake-side camping and tourism.
"We've heard that campgrounds are already fully-booked, so we know there will be a large number of people visiting and being active in and around our lakes.
"That increases the risk of the bacteria E.coli getting into our lake swimming areas by someone not using the toilet or not disposing of dog poo.
The campaign is telling lake goers to use public toilets, pick up dog droppings and use swim nappies for babies.
Environment Canterbury southern zone manager Christopher Eccleston said visitors should make sure they have gone to the toilet before they head out on the lake.
"It's a bit like what your mother used to tell you, go to the toilet before you go," he said.
"It also links into things like sensible behaviours with your dogs, just like we ask people to do in towns, pick up your dog poo."
One of the lakes, Ruataniwha near Twizel, was closed in early 2019 due to bacteria and other pathogens causing an E.coli pollution. This led to health alert measures and closures of the main lake swimming area for several days during the peak of summer activity.
Surface water science team leader Shirley Hayward said human or dog poo was a likely contributor to this event.
"Our investigation ruled in other possible contributors, such as birds, farming activity or a sewerage problem.
"Due to the fact that there was so much human activity in and around the water, it's likely that it was caused by poo.
"Human faeces are an especially concerning pollution source due to the wide range of pathogens that can be present.
"It only takes a single 'deposit' to contaminate an area because lake swimming areas are like pools - warm, shallow and without a lot of flow. One 'accident' can close the lake for a whole camping trip."