Mr Holmes said the water gathered pollution along the way, mainly run-off from roads eventually discharging into the Ruamahanga.
A clean-up plan could be to re-direct the stream by creating an open drain which would run from the hospital grounds along the town side of Colombo Rd and through a culvert to the other side of the road, discharging into the new wetland area of Henley Lake.
"This would allow the water to be processed through the reeds and other vegetation before the cleaned-up water went into the river," he said.
The stream would be kept well away from Lakeview School, he said.