The Canterbury regional council and environmental groups are awaiting sediment test results from Lake Opuha to reveal whether dangerous chemicals are buried in the lake bed.
The Opihi Catchment and Environment Protection Society (OCEPS) claim there are pesticides in the Opuha lake bed after it took tests when the lake ran dry last summer.
The council was working with the society to analyse further tests taken about a week ago.
A society spokesperson Allan Campbell said the samples were taken by a dive team from Nelson.
"The divers used GPS co-ordinates that OCEPS had provided them of sites that had very high positive samples of levels to DDT dieldrin etc, so a number of sites, about six or seven, were core sampled and these samples will be sent away to labs in New Zealand and Australia."
Mr Campbell said the results were due back in about a month, and if they came back negative, further testing must be done.
"I personally think there will be positive samples, we're very positive about that, but I think if everything came back blank, then another opportunity will have to arise where the lake level is very low and samples are done on a dry lake bed."