Coast to Coast organisers are baffled by a troubling eye condition which affected six competitors during the kayak stage and forced one to withdraw from Saturday's one-day race.
Wanaka's Peter Smallfield lost his vision and was forced to withdraw 15kms from the finish line after struggling to complete the 67km kayak stage through the Waimakariri Gorge. The 23-year-old was taken to hospital where a doctor told him his problem was a chemical injury.
Longest Day champion Braden Currie was also affected and received treatment post-race at the New Brighton finish line after losing sight in his right eye.
"It's a strange one," Currie said. "It was about 40 minutes into the kayak that I started to feel pain in my eye.
"I just started to go blurry in my right eye and had quite a lot of pain coming through and then it would come and go every 15 minutes. I'd lose my sight every once and a while and my eye would hurt quite a lot. Then it would fade away again and come right for maybe 15 minutes and then it would kick in and go again.
"Two days later I still don't have the same vision in my right eye that I do in my left eye but it will come back."
Race Director Richard Ussher is working together with relevant authorities to try and uncover the source of the irritant.
"At this stage all we know is that we have six people who have very similar symptoms," Ussher said.
"There is also some other people who look to have unrelated symptoms. Vision blurring from natural causes is a quite well documented side effect of fatigue and things like that.
"Certainly, the health and safety of our competitors is absolutely paramount so we're doing everything we can to try and find out what it is and work with the relevant authorities like DOC seeing if we can figure out what it is.
"It is unlikely it came from the river itself given the fact that in the two day race there were quite a number of people who went for unintentional swims. The vast majority of those guys haven't had any symptoms."
There has been speculation that the didymo wash (dishwashing liquid and water) used by competitors at Goat Pass to prevent contamination of the river may have been responsible, while fire retardant used to control the recent blaze at Flock Hill could be another source of the problem.
"That's very, very unlikely," Ussher said. "What they use (fire retardant) is very similar to the didymo wash that we use on Goat Pass. The detergent is a potential irritant but by the time it hits the river it would be so diluted, and it would have to come from the river, so again all those two-dayers would have got it.
"They've obviously passed through an area which has had some sort of contamination or they have, or their gear has, come into contact with something. At the moment that's what we're trying to work out, is the where and what and how.
"Between staff and competitors there were over 1000 people on the course and we're talking about six people. Until we definitively know what it was and where they got it from, we're just going to have to keep digging."
Currie was unfazed by the issue and believes it will be difficult to determine the cause.
"It's obviously something that went in my eye and no one is to blame for it," he said.
"I've heard from Richard today and yesterday and had a good chat to him about things that could have done it.
"It's going to be pretty much impossible to track down what it is."