WORLD class athletes had their triathlon downgraded at the last minute after water test results deemed the lake of a West Sussex estate unsafe to swim in.

Double Olympic champion Dame Kelly Holmes, world champion triathlete brothers Alistair and Jonathan Brownlee, and more than 700 amateur competitors were set for a swim, cycle and run around Petworth Park on Sunday.

But a water test of the seven acre lake in the National Trust grounds the day before the Macmillan Brownlee Tri South revealed toxic levels of algae.

The triathlon was ditched in favour of a back-up duathlon, with the swimming leg changed to a two km run for both the individual SuperSprint and individual sprint and team relay challenges.

This was the first year of the event, put on to raise money for Macmillan Cancer Support.

Next year it will return – hopefully as a triathlon.

A spokeswoman for event organisers Professional Sports Group said: “We were monitoring the water situation on a daily basis in the lead up to the event.

“The health and safety of competitors was our priority.

“We were also due to have two Olympic athletes, who are in the middle of their triathlon season, taking part in the swim and we could not take any risks.

“The final water test was unfortunately the first to come back stating that it was unsuitable for swimming due to a form of blue-green algae.

“As a result the event became a duathlon.”

A spokeswoman for the British Triathlon Federation said: “Blue-green algae can be a problem when the weather gets nice.

“The Great North Swim in Windermere was cancelled for the same reason four years ago.

“All good triathlon events have contingency plans.”

Dame Kelly Holmes got the fastest time in the individual SuperSprint, which involved a 2km run, a 16km bike ride followed by a 2.5km run.

She finished with a time of 49 minutes and 39 seconds.

For full results see the event’s website brownlee