Mrs Staples said the Moroa water race was "not primarily an ecological system" but the council was charged with managing it in line with the national policy standards.
Last year an attempt to combine the Moroa system with the Longwood water race under a common by-law was contemplated but that by-law was not adopted.
A consultant's report prepared at that time identified the attitudes of people using the Moroa water race to fencing it off.
Some were in total opposition and questioned how that could be done while still allowing stock access to drinking water.
Others were less opposed but were unclear as to what type of fencing would meet the needs.
Moroa water race is a man-made network that draws water from the Waiohine River along with water from the Greytown stormwater system and the Battersea drainage scheme.
It dates back to the 1890s.