Water clarity

Water clarity or turbidity refers to how clear or cloudy the water is. Clarity is important for fish to find their prey, for plants to photosynthesise and for people to be able to swim safely.

Clarity is affected by things like sediment and algae. Sediments can be soil or other small pieces of organic and geological materials. Sediments are naturally part of water bodies, but land use and weather-related events can increase the amount of sediment in the water. In the Waikato region, pest fish like koi carp stir up the sediment, reducing water clarity.

Dr Eloise Ryan talks about water clarity and sediment.

The following resources explore some of the factors that lead to reduced water clarity and ways in which we can help to prevent water from becoming turbid.

Articles

• An introduced species – koi carp

• Trapping koi carp

• Human impacts on the Waikato River

• Farming and environmental pollution

Interactives

• Healthy farms, healthy fish

• He painga mō te pāmu, he painga mō te ika

Videos

The following videos provide information about the impacts of sediment on water quality. Although some of the videos refer to marine ecosystems, the impacts are similar for freshwater ecosystems.

• Estuary issues and protection

• The effect of sediment on water quality

• Sediment research project

• Mussels filtering water

Transcript

DR ELOISE RYAN

Turbidity is the amount of sediment in water, and that determines the water clarity. Sediment is basically the amount of soil or dirt in the water – the more sediment in the water, the more cloudy it is. And people do like to swim in clear water, and our fish like to hunt in clear water, so sediment can clog their gills. And we have little animals called invertebrates living in our streams, and they are an important part of the food chain, and they get totally smothered by silt and mud and can’t survive.

Also, it depends on the geology of the stream. Some streams have more rocky or cobbly bottoms, compared to other streams that might have silty or muddy bottoms. If the stream banks are made up of a certain type of soil, that soil may break down and fill the streams with more dirt than other types that may have more rocky sides, or they may have trees that help protect the stream banks.

So there is soil always in catchments, but if you change the land use of that catchment – for example, if you cut down all the trees and you turn it into intensive agriculture – then that soil is more exposed, and so when it rains, that can wash into the waterways and increase the amount of sediment in the water, and that’s detrimental to aquatic life.

Acknowledgements

Dr Eloise Ryan
Aroha Salu
Waikato Regional Council
Invertebrate guide, Greater Wellington Regional Council
Logging footage, ACME Manufacturing Inc. Released under CC BY 3.0