A downpour of 75 millimetres in an hour on the evening of January 26 caused the containment dam wall to breach, and muddy water to surge down Googong Creek and into the pristine Upper Queanbeyan River.

That's outraged local environment groups and residents living alongside the river, who recently tested the water quality and recorded phosphorus at seven times the normal level.

Wickerslack Lane resident and Landcare volunteer Roger Clement said the spill was a major ecological concern, and cast doubt over development controls at the new township.

"There was seven times the amount of phosphorus when the Molonglo Catchment Group sampled it last Wednesday, and that can form the basis of blue green algal outbursts. It's by no means impossible that we'll see blue green algae in Queanbeyan this autumn," Mr Clement said.

"There's nothing to hold any rainfall on the site, because they've completely scalped it. It's all runoff."In my view, the only way to resolve this is to have an independent review of the Googong DCP, particularly the hydrology of it, because it's clearly failed and it looks as though it could fail again. Another two inches of rain now would probably do the same thing. It's fallen at the first hurdle," he said.

Water in the Queanbeyan River remains turbid and coffee-coloured as a result of the spill, which Dr Stephen Skinner of the Molonglo Catchment Group said will harm the local platypus population. The catchment group has written to Googong project director Mark Attiwill expressing its concerns.

"Turbidity at this level will smother aquatic plants and gilled aquatic animals including fish, tadpoles and many aquatic invertebrates that platypus feed on," Dr Skinner said.

"The mud could also cause infilling of holes in pools and riffles that would otherwise provide egg-laying sites for native fish."

Queanbeyan Landcare also lodged an official complaint with the Environmental Protection Agency (EPA), who directed them to Queanbeyan City Council as the regulatory body.

"There are no health warnings with respect to the breach of the dam. The turbidity has increased but this is a normal occurrence after heavy rains and will clear in a week or two. 

"The water from the breached dam was a small part of actual river flows that occurred with the heavy rains. The river normally becomes turbid after heavy rains and residents should always refrain from drinking from it," the spokesperson said. 

Googong project director Mark Attiwill said the developer had complied with all Council construction requirements at the site, and had strengthened the containment dam following the breach.

"The most important thing is that residents have raised a concern and we've responded to that concern. We've been in communication with them since Tuesday ... and we're reviewing the work practices on site to see if we can augment what has been approved," Mr Attiwill said.

"I think the most important thing to do is comply with our approvals, and we've done so and will continue to do so."