A routine inspection uncovered a chemical flocculent in stormwater collection ponds that may have drained into a tributary of Majors Creek. Test results are expected on Monday.

The EPA's Gary Whytcross said it was disappointing to discover potential for pollution a week after the discharge.

He said Unity Mining subsidiary Big Island Mining, which is building an underground gold mine at Majors Creek, was under investigation on whether it polluted water and breached the Protection of the Environment Operations Act.

''While BIM's attempts to treat the stormwater may have been well intentioned, the EPA is concerned about the potential impacts of the chemical on downstream waters as flocculent can be harmful to aquatic life if discharged directly into a waterway.''

Downstream landholder Jackie French said the EPA warned her late on Friday not to use water drawn from Majors Creek.

She said the flocculent manufacturer's full disclosure said it could be toxic in high concentration, but did not contain any data to measure several key health indicators.

''They know it is toxic to fish, but they are the only tests which appear to be done. The supplier's full disclosure document says tests have not been done on anything other than rainbow trout.''

Mr Whytcross said the EPA had not observed or received any reports of dead aquatic life but would continue to monitor the health of the creek and had advised NSW Health.

He said BIM had advised the EPA it had tested the discharged waters for a range of parameters but did not test for chemicals, so it remained unclear whether any chemical was discharged or made its way into Majors Creek.

Uniting Mining chief executive Andrew McIlwain said flocculent, which was used, among other things, to clean swimming pools, had been in use since the end of February. It bound together particles so fine they sometimes looked like milk. He said the stormwater was irrigated onto paddocks but to his knowledge had not been discharged into creeks.

Information on material data safety sheets had raised concerns, but those related to highly concentrated applications - as if you were putting your hand into a bucketful of the material.