More than just footprints were left behind after the Sotheby's International Realty Hawke's Bay Marathon where more than 8000 people from across New Zealand participated.
A Clive local walked part of the route along the Clive Wetlands on Saturday afternoon after all the runners had finished and picked up a 40 litre tramping bag full of rubbish.
Duncan Darroch said his bag was "full to the brim" of used and torn apart gel packs, as well as water bottles and rubbish.
The 36-year-old, who has a passion for environmental education, said the Clive Wetlands was a very sensitive ecological area.
"This has a real significance for birds that would pick those pieces up and eat them, especially the shiny bits, and would easily get into the rivers and wetlands," he said.
The section Darroch attempted to clear was about 6km of the marathon route, from Evers-Swindell Reserve to Black Bridge.
Event spokesman, Ironman Group Oceania regional director Chris Randle, said their Course Team cleared the whole course of the full marathon, half marathon and 10km.
"They drove all the areas and have physically checked the entire length of course," he said.
But, the Clive resident said he was the only one on Saturday afternoon clearing up that part of the route - picking up bottles and gel packs that the runners had dropped while they were probably in quite a "delusional" and "dehydrated" state.
After filling his bag he took it back to the main site of the Marathon and spoke to the contract manager at Close Loop recycling – which had been given the task of managing waste for the event.
"He said his contract only extended as far as the aid stations and the event site," Darroch said.
"We live in a pretty much untarnished and beautiful natural environment and the Clive Wetlands are pristine and we'd really like to keep it that way," he said.
All competitors in the 10km, half marathon, and marathon were given race packs which included gel packs, he said.
"Eight-thousand were given out at the start and so it was a natural consequence that people would be using them," Darroch said.
Randle said, due to the course size, the tidying process can sometimes take a little time, but they work diligently to leave as "small trace behind as possible".
The regional manager said the team was back on the course on Monday double-checking all areas.
Darroch said by Monday it could be too late as smaller bits of plastic would already have been picked up by the local birdlife or fallen into the waterways.
Randle said the Hawke's Bay Marathon had implemented a number of sustainability initiatives, including partnering with Closed Loop, which provided sustainable waste management and cleaning.
"The event also uses a mix of PRET recyclable, PE recyclable and PLA Biodegradable cups, and 95 per cent of plastic cable ties that are used to secure signage have been replaced with re-usable bungee cords," he added.