Secret Defence reports obtained by The Canberra Times showed the 143ha Lawson site was heavily contaminated by toxic waste. They raised concerns that high levels of heavy metals had been found in Lake Ginninderra sediment and water samples.

ACT Chief Minister Jon Stanhope said yesterday there was no risk to lake users.

''We do test the waters of our lakes regularly to ensure they're safe,'' he told ABC.

''At no stage has any advice been given to me or the ACT Government that there are any issues or safety issues except those seasonal ones of algal bloom that we have from time to time.''

Environment ACT's director of Environment Protection and Heritage, Robert Neil, said he would order new tests today, and go back over past results to ensure those tests had been looking for the right things.

''I'm fairly confident that this is confined to the site, but we'll check it again ... The water quality out there is very good, which is why I'm very surprised [by the reports],'' he said.

Mr Neil said he had seen reports on the site previously, but not to the level of detail revealed in the Snowy Mountains Engineering Corporation reports.

Some contamination was to be expected at a past industrial site, such as this, and he did not expect cleaning the site would create huge problems, although it would be expensive and could take some time.

Defence, as the polluter, would have to clean the site before anything was done with it. There was a ''fairly extensive process'' involving appointing a registered and independent contaminated land auditor, whose report would be analysed by the Environment Protection Authority, before the land use could be changed.

The federal and ACT Greens have been highly critical of Defence over the matter, but ACT Liberal senator Gary Humphries is accusing them of ''naked scaremongering'' and telling an ''absolutely outrageous untruth'' to try to win votes in the ACT election.