A report presented to the Otago Regional Council earlier this year showed the water quality of the Cardrona River and its tributaries was "generally very good".
The exception was Spotts Creek, the mountain stream that runs through Mr Mackay’s Spotts Creek Station and into the Cardrona River.
The creek had elevated nitrogen concentrations, and E. coli counts at "red-alert" levels on several occasions, the report said.
Mr Mackay said yesterday while that might have been the situation in March 2015, he had no qualms about drinking the water now.
"We’re unsure of exactly what [the cause] was.
"It could have been anything and a likely cause could have been that it was a dead animal in the creek."
"A small spike like that shouldn’t paint the picture of it being a dirty creek because it’s not.
"It’s a very clean creek."
In an explanation of the council’s monitoring of Spotts Creek, director, policy planning and resource management, Dr Gavin Palmer said the results were "a snapshot" designed to help identify trends.
"While the levels of E. coli observed in Spotts Creek exceeded safe levels for swimming on a number of occasions in 2014-15, the levels observed in the Cardrona downstream were consistently at levels considered safe for swimming."
He warned people should always be wary of drinking from streams and rivers as there could be "unanticipated factors" affecting water quality on any given day "for example the presence of dead animals in the creek or giardia".
Spotts Creek is on the route of the two-day Defiance multisport race, with more than 300 athletes likely to follow it and cross it on their way to the top of Mount Roy on January 22.
Race organiser Sally Currie said while there were no health issues among athletes in the last event, those entered in the January event would be "strongly" advised not to take water from any waterways.
"We do provide nutrition and water at each transition, so there is no need for competitors to take water from the streams or creeks during the competition."
Mr Mackay said he was training to be a first-time competitor in the event.
