The decision to call the swim off was communicated soon after the 10km swimmers began their first of what should have been four 2.5km laps of Ruby Island.
Swim directors Eddie Spearing and Jamie Norman said experienced 10km swimmers reported to marshals at the end of the first lap they were struggling with the waves, being flipped on their backs, and struggling to get around the top of the island.
About 50 swimmers were in the 10km category, which began first at 7am when conditions were flat and calm.
Other, shorter distances from 5km down to 200m, were due to start throughout the morning.
Mr Spearing said a chop soon picked up and "it just got worse and worse".
"Some did two laps and most did one lap and it became very evident we could not put anyone else in the water and had to pull the pin.
"Our safety team made the decision. The kayakers and jet skiers could not do their thing. It was an easy decision in the end but not one we took lightly," Mr Spearing said.
Water safety officer Craig Fahey said conditions were "pretty benign" at the start.
"It came in pretty quickly and by the time we made the call half way through the first lap of the 10km we were looking 1.5m swells and probably 20 knots of breeze, which made it pretty difficult for the rescue support people to be able to effectively support the race."
A handful of swimmers got in the water to test the conditions and were warned they were swimming at their own risk.
Richard Collins of Alexandra, reported he enjoyed his swim and did not mind rough conditions. But agreed the event had to be canned.
"It was pretty rough. You would expect to get knocked around out there. The event organisers made the right decision to can the race. . . . I have probably swum in bigger waves but the wind was just relentless and you have got to be prepared to take on water and go down for a few cycles."
Mr Collins said he found it "really hard" to get around the back of the island, but once there felt "sweet" sticking close to the shore.
The crossing to the Ruby Island was also very rough, he said.
Mr Norman said the cancellation was the event’s second.
"Our first was our first year and this is our 10th year, so therefore this is only going to happen every 10 years," he said.
Mr Norman said the organising team and volunteers "gave it everything we could" and were proud of what they had done.
"The lake has won. The lake is going to get the rings this time, for the second time," Mr Norman said — referring to a decision made in 2015 and again on Saturday to consign the 2.5km first prizes — a pair of rings — to the deep.
