"It was [a] flukey shot really, that I managed to get him with such a clear expression on his face.
"It was literally a spur of the moment. Mason was just playing in the water with his poppa - my husband Kerry - started throwing him into the air."
The family heads to Kai Iwi Lakes each summer and Anderson said they had only just returned home.
Anderson said she was "pretty stoked" she had won the competition and since hearing the news, Mason's dad has already put his hand up for her old camera.