The Victorian state government says it is unable to rule out of a repeat of the North East Link chemical leak that turned a Melbourne waterway bright blue.

Project bosses insist the substance that leaked into a Rosanna creek is safe, but the environmental watchdog says they don’t even know what the chemical is yet.

Early reports from the EPA indicate the leak is a polymer used as a dust suppressant at the nearby construction site.

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But its exact chemical makeup remains unclear.

In a statement to 7NEWS the Government’s Major Roads Authority says there is “no threat to the community — or the environment”.

The North East Link project — a 10km expressway which will connect Melbourne’s Metropolitan Ring Road and the Eastern Freeway — has been plagued by environmental concerns.

“You know, this has been ongoing for five years,” public transport minister and former opposition leader Matthew Guy said.

“It looks like an environmental catastrophe out of East Germany in the ‘80s.

“At the moment there’s radio silence from the government.”

Residents have previously raised the alarm over dust, noise and light pollution.