Secchi Depth Calculator

Water clarity measures how transparent water is, indicating ecosystem health. Clear water allows sunlight to penetrate deeper, supporting aquatic plant growth and oxygen production. Poor clarity can indicate pollution, algae blooms, or excessive sediment.

Lower a black and white Secchi disk into the water until it disappears from view. The depth at which it vanishes is the Secchi depth. If there's current causing drift, measure the rope angle and calculate the true vertical depth.

Secchi depth indicates water transparency. Values over 3m suggest very clear water, 1-3m is moderately clear, 0.5-1m is murky, and under 0.5m indicates very turbid water. Each water body has natural baseline values.

Secchi depth is better for deep lakes and oceans, while turbidity meters work well in shallow or flowing water. Secchi depth gives a practical measure of light penetration, while turbidity provides precise particle concentration data.

The photic zone is the water depth where at least 1% of surface light remains. This zone determines where photosynthesis can occur. Deeper photic zones support more diverse aquatic ecosystems and better water quality.

Water current causes the rope to drift at an angle, making the measured rope length longer than the actual vertical depth. Use trigonometry to calculate the true depth: true depth = rope length × cos(drift angle).

Recent rainfall, algae blooms, suspended sediment, natural water color, construction activities, and seasonal mixing all affect clarity. Take baseline measurements over time in the same location for accurate monitoring.

Swamps and ponds typically show <0.5m, murky lakes 0.5-1m, typical rivers 1-2.5m, clear lakes 2-5m, and very clear mountain lakes or tropical waters can exceed 10m. Natural factors like tannins can reduce clarity in healthy ecosystems.