People are being urged to take extra care around the banks of the Hutt River after medical waste was found in there last Friday.
Used needles, liquid medicines and expired tablets were picked out of the Hutt River near Ewen Bridge.
Hutt City regulatory services manager Geoff Stewart says they need the public's help to make sure it doesn't get further downstream.
"It has definitely moved down the river and we're unsure how far that could've gone down, so if there is any containers found if they can bring them back to Hutt City Council that'd be really good."
Mr Stewart said the council was investigating where the waste came from and police had been notified.