Maximum increase of 10 NTU's
Natural influences that cause the turbidity of a stream to change:
- Geology - the types of material in the area where the stream flows affects turbidity (e.g., banks with loose soil will cause more erosion).
- Stream size - large rivers may have many microscopic plants that increase turbidity.
- Seasonal weather - spring snow melt and rain can increase runoff which generally also increases turbidity.
- Plant root systems - roots help hold soils in place and out of the river. Fires, floods, wind storms, and other natural events may take out this vegetation which would increase erosion and turbidity.
Human influences that cause the turbidity of a stream to change:
- Bank stabilization - maintaining riparian vegetation or installing rip rap can help decrease turbidity.
Activities that will increase erosion:
~ Road building
~ Deepening or dredging channels
Why care about turbidity?
Suspended solids prevent sunlight from reaching aquatic plants. Without light photosynthesis cannot take place, which may reduce the amount of dissolved oxygen in the water. Dissolved oxygen is vital for fish and other aquatic life. Sediment absorbs heat, so turbidity can raise the surface water temperature. Turbidity can can also make it hard for fish to see their prey. Heavy loads of suspended solids can even clog fish gills and filter-feeding devices of aquatic macroinvertebrates (water bugs). As solid matter settles, it may cover and harm bottom-dwelling plants and animals and spawning beds. However, turbidity isn't always bad. All streams have a natural level of turbidity. While some forms of aquatic life need clear water to survive, other aquatic species are adapted to and thrive in high turbidity. The Colorado River is very turbid, yet its waters hold abundant life.