The river has the worst water quality of all the Christchurch rivers according to CCC, but it is not all gloom! The Cashmere Stream and Steamwharf Stream which are important tributaries have water quality ratings of GOOD.
Contaminant levels change along the length of the river due to environmental factors. CCC and ECAN take monthly samplings at 15 sites within the Ōpāwaho Heathcote River catchment. You can access these water quality test results on two websites: on the recently released Wai Map: Ngā wai o Ōtautahi-waterways of Christchurch or on the Land Air Water Aotearoa (LAWA) website. Each displays the results in different ways.
The results show that overall, the river is in poor health, but there are aspects of its water quality that may be improving. The results vary along the river due to local conditions.
Sediment is soil particles washed into the river largely, but not exclusively, from the Port Hills. Sediment smothers the habitat of macroinvertebrates and fish, reduces visibility and introduces excess nutrients into the waterway. Sediment is a particular problem in this catchment because the hill soil is “loess” – very fine grained, easily eroded and hard to control. Saltwater is a flocculant for it meaning that saltwater causes the loess to come out of suspension and deposit in the estuary. This makes sediment a problem for both the river and the estuary.
Dissolved zinc is largely the result of water runoff from unpainted/old exposed zinc roofs and gutters or from road runoff as a result of tyre wear. It is toxic to instream biota.
Dissolved copper enters the waterway from two sources: a) copper worn off car/truck brake pads which would easily be avoided if the available copper-free brake pads were used. b) water runoff from copper roofs and gutterings also contributes to the problem. Dissolved copper is toxic to instream biota.
Bacteria prevents use of the water for recreation and can cause serious ill-health. The source includes avaian (birds) but also dog source e coli is a significant issue with any rain event and wastewater overflows contribute sewage following significant rain events. Longer riverbank grasses and planting reduces e coli.
nitrate, nitrite, ammonia, organic nitrogen, phosphate, total phosphorus
The nitrates are from farming. The nitrates are highest in the source springs, and actually decrease as you go down the river. Farming controls in the unconfined aquifer is the solution. Excessive nitrates increases sediment problems as it encourages higher weed growth which it turn slows water and causes sediment to precipitate.
Take a look at the actual water quality testing results for this river
This term describes the ecological degradation of streams draining urban land caused mostly by stormwater runoff but also sewer overflows, wastewater treatment plant effluents, and legacy pollutants.
