Water and sediment from a South Canterbury lake is to be sampled again, after allegations that dangerous pesticides are buried in the lake bed.
Canterbury Regional Council has confirmed it is planning further sampling from Lake Opuha, near Fairlie, over the claims.
The Opihi Catchment and Environment Protection Society (OCEPS) said tests of sediment samples it took have revealed extremely high traces of the now banned agricultural chemicals, DDT and dieldrin.
This issue dates back to 2011, when claims were made that during construction of the Opuha dam in the late 1990s, drums containing agrichemicals had been buried under the area now covered by the lake.
While a survey found no evidence to back up the claims, the issue raised its head again earlier this year when the summer drought caused the lake level to fall, exposing much of the lake bed, including the area originally identified as a dump site.
That allowed Environment Canterbury (Ecan) to carry out a fresh investigation, which once more failed to find any signs of buried drums of pesticides.
But OCEPS campaigners said the environmental watchdog was looking in the wrong place and tests the society had done on sediment samples from the lake bed revealed very high levels of DDT, as well as the presence of dieldrin.
Officials have followed that up with further tests of water from the lake and river system, finding no signs of contamination.
But in a final effort to get to the bottom of the case, Ecan is now arranging for specialised equipment to do yet more sampling.
Ecan is hoping for a meeting with OCEPS members this week, and said it will make sure representatives from that group are involved in the resampling work.