Mining giant, Rio Tinto has been fined $50,000 over the collapse of a dam wall at it's Mount Thorley Warkworth Mine near Singleton.
Hundreds of thousands of litres of water escaped from the dam when the incident occurred in January last year.
The company blamed the collapse on several days of heavy rain.
The Land and Environment Court ruled that while harm from the incident was insubstantial, the failure of the dam was both forseeable and preventable.
