How deep a lure runs, and what controls it

THE STATED DIVING DEPTH ON A LURE IS A RESULT OBTAINED UNDER PARTICULAR CONDITIONS, and almost every condition in fishing differs from them.

WHAT SETS THE DEPTH OF A DIVING LURE.

THE LIP. Size and angle. A larger lip catches more water; a lip angled more steeply downwards drives the lure deeper for a given speed. This is the property the manufacturer chose and the only one you cannot change.

RETRIEVE SPEED, and it is not linear. A diving lure needs enough speed to make the lip work, so up to a point faster is deeper. Past that point the lure begins to plane and rise, and beyond it may blow out entirely. There is an optimum speed for maximum depth, and going faster than it makes the lure shallower.

LINE DIAMETER, which is the factor most often ignored and one of the largest. A thick line has more drag in the water and lifts the lure; a thin line lets it run substantially deeper. The difference between heavy monofilament and thin braid on the same lure can be a metre or more.

CAST LENGTH. A lure reaches its maximum depth over the middle portion of the retrieve, after it has had distance to dive and before the angle to the rod tip starts lifting it. A short cast never reaches the depth a long one does.

ROD TIP POSITION. Held high, the line angle lifts the lure. Held low, or with the tip in the water, the lure runs deeper. This is free depth and costs nothing.

WHAT SETS THE DEPTH OF A SINKING LURE, which is a different problem. Here it is the fall rate and the countdown: mass and shape set how fast it sinks, and the angler sets how long it is allowed to. A count before starting the retrieve is the most reliable depth control in lure fishing and one of the least used. The retrieve then decides whether it holds depth, climbs or continues down.

AND IN CURRENT, ALL OF IT CHANGES. Flow lifts a lure worked against it and a lure worked across it. In a river the same lure and the same retrieve will run at different depths on each cast as the angle to the current changes through the swing, which is why depth control in flowing water is a matter of angle and mend rather than of lure choice.

THE PRACTICAL CONSEQUENCE. If the fish are not where the lure is, the cheapest fixes in order are: lower the rod tip, lengthen the cast, slow to the optimum speed rather than the fastest, and thin the line. Changing the lure is the expensive option and it is where most anglers start.