Principal rural fire officer Myles Taylor said the fire, which covered about 0.5ha, was called in by the Department of Conservation when a ranger spotted it from the water. The Fire Authority was investigating, he said.
Mr Muster, who dominated clay courts in the 1990s, bought a 37ha Long Beach property late last year for $5.65 million.
Meanwhile, the Kerikeri Fire Brigade was called to State Highway 10, near the intersection with Kapiro Rd, after a car caught fire at noon yesterday.
The vehicle was burning fiercely when the brigade arrived to extinguish it. It was then left in the hands of the owners and their insurance company.