Turbidity
Turbidity is how cloudy or murky water looks when tiny bits of dirt float in it.
A glass of water sits on a counter, perfectly clear. Stir in a spoonful of flour and the water turns white and cloudy. The flour particles float throughout the glass, blocking light from passing through. The more flour you add, the cloudier the water gets.
Explaining turbidity by grade level
A creek can look clear or murky. Dirt and mud make the water hard to see through. More bits in the water make it look darker. Fish need clear water to find food and stay safe.
Projects that explore turbidity
Rain washes soil, fertilizer, and fine debris off nearby land and into creeks and rivers. When you measure that cloudiness with a turbidimeter, the reading reflects how many tiny particles are floating in the water. Wenas Creek, which flows through a more developed area, showed higher turbidity and nitrate levels than Umptanum Creek — suggesting that human activity raises the particle load in nearby waterways.
Cloudy water and dissolved oxygen might seem unrelated, but testing them together reveals something unexpected. You collect samples from different spots in a river, measure turbidity with a turbidimeter, then determine dissolved oxygen by counting drops of sodium thiosulfate until the yellow color clears. Samples with higher turbidity actually had higher dissolved oxygen — the opposite of what most people would predict, and a result worth further investigation.
Storm drains, construction sites, and eroding banks all add fine particles to flowing water, raising its cloudiness. Collecting five samples upstream and five downstream from a populated area lets you compare turbidity meter readings directly. When human activity is concentrated in the middle, that comparison can flag changes in water quality that are invisible to the naked eye.
Gravity pulls heavier suspended particles downward over time, so cloudiness does not stay uniform from top to bottom in a lake. Near the surface, wind and waves keep fine sediment stirred up. Deeper water is calmer, letting particles settle — and a turbidity meter can capture exactly how much the readings shift as a diver descends from 1 meter down to 4 meters.