The Northern Territory's Amateur Fisherman's Association says it has serious concerns about an uncontrolled discharge at the Mount Todd mine near Katherine.
On Friday, the mine's operator Vista Gold notified the Environment Protection Authority of a leak of untreated contaminated water.
The association's Craig Ingram says the discharge will have some impact on the Edith River and also highlights the need for improved infrastructure.
"The retention pond's clearly not big enough or systems in place to deal with spills," he said.
"So any uncontrolled discharge like this particularly in small rain events like this one clearly highlights that we've got issues at the mine which haven't been addressed and aren't being addressed and probably just been ignored in the past." Mr Ingram says the leak should never have happened.
"The size and quality of the infrastructure wasn't sufficient to control the fairly small rain event," he said.
The Environment Protection Authority is investigating the spill.