Colour and water clarity
A lure’s colour matters for exactly as long as it can be seen. Water clarity is a distance, not an impression, and it can be measured.
The Secchi disc
The classic method: lower a white disc into the water and record the depth where it disappears. That depth is the clarity. The method is old, simple and repeatable — hydrologists still use it, and for the same reason it works with a metal lure on a line. A standard disc is 20 centimetres across, marked in black and white sectors. Measure in the boat’s shadow, not against the sun: surface glare eats up half the result.
What that means for a lure
If the disc disappears at half a metre, the fish won’t see a lure any further away either. Everything beyond that limit doesn’t exist for the eye — all that’s left there is the vibration a lure sends out around itself.
Three different causes of turbidity
Suspended clay and silt dampen everything indiscriminately. Algal bloom tints the water green and scatters light of its own. Dissolved organics from peat bogs turn the water brown. These are three different optics, and a lure looks different in each of them.
The colour of the water itself is the background
A lure is never seen on its own, only against a background. Green bloom water, brown tannin-stained water and grey clay water each give a different background, and the same lure contrasts differently against each one. The background decides at least as much as the lure’s own colour.
Algal bloom is a special case
At the peak of a bloom, clarity drops to a few dozen centimetres, yet the water stays pale. A silhouette reads worse against that background than in dirty clay water, where the background is dark and any shape on it stands out.
Clarity and depth are different things
A shallow in murky water can be darker than a depth in clear water: in the first case particles dampen the light, in the second the water column itself does. So “shallow” doesn’t mean “visible”, and the retrieve depth doesn’t guarantee light either.
Clarity changes day to day
Rain, a wind-driven surge, a dam release, a shoal of carp rooting in the shallows — and yesterday’s reading is no longer valid. A tributary clouds fastest after a downpour: its mouth can be muddy while the main channel stays clear. Clarity is checked on the spot, not remembered from before.
What’s in this section
Two cards. The first is about how clarity changes the choice of colour. The second is about two opposite logics of that choice: matching the forage, or deliberately matching nothing at all.
