State of the River

Sediment

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.

Zinc

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.

Copper

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.

E. coli

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.

Nutrients

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.