A firefighting boat has been called to help three Metropolitan Fire Service and Country Fire Service units contain a blaze at Hume Reserve, Murray Bridge.
The fire started in reeds at the northern end of the reserve around 9.45 on Sunday morning.
When firefighters arrived, they found the flames difficult to reach.
A State Emergency Service boat was summoned to assist from the water.
Despite the orange flames leaping two metres high, dense black smoke and growing crowd of onlookers on a nearby ridge, fisherman Franko Vasile was not concerned.
He continued to sip his drink and monitor his lines as the battle raged a dozen metres away.
“I was here 15 minutes before it started and then suddenly the fire come up,” he said.
“I thought maybe someone is lighting grass or something like that.
“Definitely someone come from other side; from this side you cannot go anywhere there.”
However, he could not be sure the fire had been deliberately lit.
Police also attended the scene of the fire.
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