Researchers from the Cawthron Institute will monitor red dye to be spilled into Picton's sewerage system to test the town's new outfall pipe.
Marlborough District Council hired the institute to release the tracer dye into the system to gather dilution factor information for the wastewater coming out the new pipe, partly by monitoring the dye's ability to spread in the harbour.
The dye may be visible for up to five hours but is not toxic.
A council spokeswoman said a council preliminary test last Thursday did not show up in the harbour because the dye was too diluted.
- The Marlborough Express