Freshwater environment
How healthy is Auckland's freshwater?
- As with any major city, the health of Auckland's freshwater environment varies across the region, with pristine areas in the forested ranges of Waitakere and Hunua, and degraded systems in heavily urbanised or industrial areas of Auckland.
- Streams in native forest catchments like the Cascades in the Waitakere Ranges have the best
water quality and ecological health, with natural habitat, stream flows, and low levels of contaminants. By comparison, streams in urban areas often have modified habitats and stream flows, and urban stormwater contaminants. - Lakes Ototoa and Pupuke have high water quality, with consistently high water clarity, and low levels of suspended solids and the plant nutrients phosphorus and nitrogen. Algal blooms are uncommon. Lakes Kereta, Kuwakatai and Spectacle have degraded water quality with low water clarity, high nutrient levels and frequent algal blooms.
- Wetlands in Auckland region are remnants of large systems that existed before land was developed for agriculture or urbanised. Those that remain are typically healthy but remain vulnerable to changes to water levels, invasion of exotic weeds and pests and fire.
What affects our freshwater environment?
- There are many environmental issues associated with a growing population, like Auckland's, in a coastal area.
- The health of freshwater systems is closely linked to the catchments they drain. The level of impact tends to increase as the intensity of landuse increases.
- Stormwater is a source of contaminants in urban environments. The toxicity of stormwater contaminants can affect macroinvertebrates and other animals living in freshwater environments.
- Vehicles are a major source of pollutants, but other factors like roof runoff and industrial discharges also contribute.
- Sediment runoff from land development, agricultural practices and stormwater also affects the freshwater environment.
- Sediment can smother and kill freshwater organisms or make areas unsuitable for some to live.
- Too much sediment in the water column can reduce water clarity and light penetration which can reduce the productivity of freshwater ecosystems.
- Most lakes in the Auckland region have been influenced by vegetation clearance, farming and/or urban development within their catchments.
- Lakes located within farming catchments generally have high levels of nutrients which can affect water clarity and promote harmful algal blooms.
- Some groundwater aquifers in the region suffer the adverse effects of too much water use, where the amount of water taken exceeds what is replaced naturally. The amount of water taken varies by season with a much higher demand occurring during summer when water is irrigated onto pasture and crops. Too much abstraction can affect stream flows too.
- Many freshwater environments are affected by introduced plants and animals . Submerged aquatic weeds such as oxygen weed escaped from aquariums and is now commonly found in many streams and lakes, and often replacing native plants and clogging waterways. Exotic fish are found in many streams and lakes, which in some circumstances affect native plants, fish and even water quality.
