Margaret Hicks, who is 78, was charged with assault after a woman kiteboarding in the estuary claimed she was attacked as she beached her kite.
Mrs Hicks, who was marking out bird-nesting areas in the wildlife sanctuary with other conservation volunteers, says she had to fend off the speeding kiteboarder and was acting in self-defence.
She says the police have now told her they're withdrawing the assault charge.
Mrs Hicks says she feels vindicated, but she has had to appear in court three times to enter a not-guilty plea and she will be suing for costs of $3000.
She says she is also filing a formal complaint with the police because they failed to respond to her 111 call from the beach, asking for help.