---
source: https://iinventedlight.com/library/notes/turbidity.md
title: "Turbidity: measuring how clear water is"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "US government work, public domain; restated in our own words"
attribution: "Summary by iinventedlight (AI-assisted). Sources: USGS, Turbidity and Water, US government work, public domain; USGS, Sediment and Suspended Sediment, US government work, public domain."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No observation or experiment was done; only the fetched government pages were read."
category: coverage-gaps
topic_area: "earth science: water quality"
tags: ['usgs', 'water-quality', 'turbidity', 'sediment']
sources:
  - id: S1
    title: "Turbidity and Water"
    publisher: USGS
    url: https://www.usgs.gov/special-topics/water-science-school/science/turbidity-and-water
    accessed: 2026-11-04
    license: "US government work, public domain"
  - id: S2
    title: "Sediment and Suspended Sediment"
    publisher: USGS
    url: https://www.usgs.gov/special-topics/water-science-school/science/sediment-and-suspended-sediment
    accessed: 2026-11-04
    license: "US government work, public domain"
---
# Turbidity: measuring how clear water is

**Answer:** Turbidity is the measure of relative clarity of a liquid. It is a measurement of the amount of light that is scattered by material in the water when a light is shined through a water sample. The higher the intensity of scattered light, the higher the turbidity.

## What makes water turbid

Materials that cause water to be turbid include clay, silt, very tiny inorganic and organic matter, algae, dissolved colored organic compounds, and plankton and other microscopic organisms. Rocks as small as tiny clay particles and larger that are moved by the water are called sediment.

## How it is reported

Turbidity is reported in nephelometric turbidity units (NTU). During periods of low flow, many rivers are a clear green color, and turbidities are low, usually less than 10 NTU.

## Why storms raise it

- During a rainstorm, particles from the surrounding land are washed into the river, making the water a muddy brown color.
- During high flows, water velocities are faster and water volumes are higher, which can more easily stir up and suspend material from the stream bed.
- Fast-moving water can pick up, suspend, and move larger particles more easily than slow-moving waters.
- So much sediment is carried during storms that over one-half of all the sediment moved during a year might be transported during a single storm period.

## Why it matters

High concentrations of particulate matter affect light penetration, ecological productivity, recreational values, and habitat quality, and cause lakes to fill in faster. Particles also provide attachment places for other pollutants, notably metals and bacteria, so turbidity readings can be used as an indicator of potential pollution in a water body.

## Claims
- id: C1
  claim: Turbidity is the measure of relative clarity of a liquid.
  source: S1
  evidence: "Turbidity is the measure of relative clarity of a liquid."
- id: C2
  claim: Turbidity is measured in Nephelometric Turbidity Units (NTU).
  source: S1
  evidence: "Turbidity is measured in Nephelometric Turbidity Units (NTU)."
- id: C3
  claim: Suspended sediment is an important factor in water quality.
  source: S2
  evidence: "Suspended sediment is an important factor in determining the quality of water."

## Sources
- [S1] Turbidity and Water. USGS. https://www.usgs.gov/special-topics/water-science-school/science/turbidity-and-water . License: US government work, public domain. Accessed 2026-11-04.
- [S2] Sediment and Suspended Sediment. USGS. https://www.usgs.gov/special-topics/water-science-school/science/sediment-and-suspended-sediment . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).