Intermediate lines are mostly slow-sinking lines so we might assume we use them to sink flies to fishing depth. We can use them for that, but that’s not the only reason for owning an intermediate line. The name gives a clue to what these are – they fall between fast sinking and floating lines. While trying these lines I found myself wondering if the fishing difference between a slow intermediate and a floating line was enough to justify buying one. Similarly the fastest fast intermediates now sink at about the same rate as medium sinkers – I have a medium sinker, do I need a fast intermediate line?

Density and profile
Leaving aside the intricacies of taper and core, if two fly-lines are equal in weight (same line-weight), low-density (floating) equals a fat line, high-density (sinking) equals a thin one.

How line-density affects our fishing
Lines of the same weight, but different density, behave slightly differently in the air. We might say thin, dense lines cut through air more easily than fat, floating lines. Of course, we mean a thinner, denser line presents a smaller surface area to the air, so there is less drag or air-resistance slowing the line. The net effect is that it takes less effort to cast a dense line, and in windy conditions, compared with a floater, casting can be noticeably easier, longer and more accurate.

A floating line sits on the water surface, intermediate lines, even the slowest sinking (ie, least dense) sit in the water surface. In windy conditions, fly lines on water are blown about by wind and carried by wind-driven surface currents. By contrast, intermediates sit in water, where wind, either directly or as surface current, has less effect. Net result, if a line is cast onto water across the wind, a floating line may belly and drag the flies while an intermediate line can remain straighter longer and that means our flies are fishing for longer.

How it affects our casting
For me the keys to how a line casts are head-length, rear-taper length and running-line thickness. For example compare two lines: one has a short head, short rear-taper and thin running-line, the other has a long head, long rear-taper and stout running-line. Casting to 80ft, my short head example lets me false cast about 40ft of line, then a powerful delivery to try and shoot line and reach the target. The long head line lets me false cast 70ft, my stroke is longer, and of course I only need to shoot 10ft to reach the target so there’s no need for a more aggressive delivery stroke. Which sounds like the long belly wins? Smoother casting, shorter shoot, so greater accuracy. Well, try a real fishing situation, with trees 50ft behind and a nice brisk side-wind. I try to thread the long belly between trees and hope for a lull in the wind. Meanwhile, the short belly line has plenty space for me to cast in, but for the sake of accuracy I’m still hoping for a lull in the wind.

Under scrutiny
For this group of intermediates we had to settle on a line weight so we asked for #7 lines. Any figures or measurements are for those lines, and may differ for other line-weights. I used a couple of rods during the testing, both 10ft #7 both rods I know well, both light, powerful, fast-action modern rods.

Vision Attack
Colour: Clear
Line length: 88ft (27m)
Head length: 33ft (10.1m)
Sink rate: 2 inches per second (fast intermediate)
Loops: No
Price: £29.99
From: Vision stockists
Comments: Tying on backing with a nail-knot pulled off the coating, which seems soft, exposing the mono core. Easy enough to tie a loop in the core and attach the backing. Not convinced the head is as short as the box says, maybe a few feet longer. However, this is comparatively short head, the thin running line shoots freely, roll and Spey casts nicely. Overall a handy line when space is a little limited and it handled well in windy condition. Fishes deep.

Rio Lake Aqualux
Colour: Clear/transluscent green
Line length: 100ft (30.4m)
Head length: 44ft (13.4m)
Sink rate: 1.5 to 2 inches per second (fast intermediate)
Loops: Welded loop at the tip
Price: £59.99
From: Rio stockists
Comments: Fairly supple line not as glossy as some clear lines, the coating feels firm and it carries and shoots well. Medium head length, so the Aqualux worked well when I was seated in a boat. The firm running line encouraged carry, so distances were good. From a drifting boat, with drogue and a moderate breeze the Aqualux fishes deep.

Rio Lake Camolux
Colour: Camo
Line length: 100ft (30.4m)
Head length: 44ft (13.4m)
Sink rate: 1.5 to 2 inches per second (fast intermediate)
Loops: Welded loop at the tip
Price: £59.99
From: Rio stockists
Comments: The ‘camo’ effect means the line has lighter and darker bars, like sections have been stained. In use, very similar to the Aqualux. At one point I wondered if the Camolux was a little less free shooting, as if the coating was clinging to the rings, however I now believe that was nothing more than using the two lines at different times in slightly different conditions. Fishes deep.

Cortland 444 Classic
Colour: Clear
Line length: 90ft (27m)
Head length: approx 36 ft (11m)
Sink rate: 1.5 to 2 inches per second (fast intermediate)
Loops: No.
Price: £49.99
From: Cortland stockists
Comments: Sort of a hybrid line, the 444 has an opaque braided core and translucent coating. Smooth, supple, but a slightly wiry feel to the line. Head length is at the shorter end of this narrow spectrum and that was reflected when casting for distance and the 444 does not encourage me to false cast with a lot of running line in the air. The length of head and running line I can comfortable false-cast suits sitting in a boat and also works well on banks. Shoot is good, not extreme. The 444 feels a little light on some of my more powerful rods, probably due to the restricted carry. Fishes deep.

Rovex Radion
Colour: Claret
Line length: 106ft (32.5m)
Head length: 30ft (9m)
Sink rate: Fast intermediate
Loops: No
Price: TBA
From: Rovex stockists
Comments: Few details are available with this line so the sink rate is based on my impression on water.
Exceptionally supple, no coil memory, smooth line. The Radion has a short head, thin running-line and fairly fat tip. Loads a rod easily, shoots well, doesn’t like a lot of carry, punchy turnover – at times a tendency to kick over and tug the leader back. With practice the tip turns over with leader straightening punch rather than a kick. Not a long casting line, best where space is limited.

Orvis Wonderline
Colour: Amber
Line length: 90ft (27.4m)
Head length: 53ft (16.1m)
Sink rate: 1 to 1.5 inches per second (slow intermediate)
Loops: Fitted at the tip
Price: £59.99
From: Orvis stockists
Comments: A very smooth, slightly oily feel’, wiry in the hand. This has a reasonably long head I can carry into the running line. The running-line is fairly thin, so shoot and distance is good. This is a slow sinker, meaning it often needs to be encouraged through the surface film. That hesitation at the surface seems to encourage the belly to sink first. The sink rate compares with a neutral density line, but I prefer a more supple neutral density for a slow retrieve and a more predictable sink.

Snowbee XS ND
Colour: Mustard
Line length: 90ft (27.4m)
Head length: 42.5ft (12.9m)
Sink rate: Very slow
Loops: No
Price: £45.00
From: Snowbee stockists
Comments: Supple line. On a rod this feels very much like a thinner XS floater, so it’s a little faster through the air. Head length is moderate, shoot is good, not extreme. I can carry well into the running line when I need distance, otherwise I think I work with the head just outside the rod tip. That flexibility makes the XS-ND a good general purpose line. Tactically, this a very useful fishing line for buzzers and nymphs. Fishes shallow.

Hardy Mach
Colour: Clear
Line length: 105ft (32m)
Head length: 50ft (15.2m)
Sink rate: 1.25 to 1.75 inches per second (medium intermediate)
Loops: No
Price: £54.99
From: Hardy stockists
Comments: Supple and very slick, fairly glossy finish. The Hardy Mach taper is more complicated than many of the lines in this group, designed to put a slightly higher proportion of the line mass near the front of the belly. The idea is that makes for easier casting with a short line and delays turnover when shooting line. In truth, I would be hard pressed to say I noticed easier loading. The Mach is a long casting line, but I needed back-cast space to get that long head working. The medium intermediate sink-rate and need for casting space would incline me to use a Mach from the bank, or on calmer days from a boat – I preferred more modest head-lengths in high winds. Fishes medium depths.

Barrio GT90
Colour: Green
Line length: 90ft (27.4m)
Head length: 90ft (27.4m)
Sink rate: 1 to 1.5 inches per second (slow intermediate)
Loops: No
Price: £24.00
From: www.flylineshop.com
Comments: Supple line, little or no coil memory, cuts through wind, turnover is punchy. Technically the GT90 has a 90ft head, all the running line tapers – in use this feels like a long belly line. The design allows me to carry a very long line for distance or carry less and shoot well. Actually, carrying 50ft of line I found shoot is slightly less efficient than a conventional WF with a thin running line and more average belly length. Nonetheless, on my rod, the GT90 is the longest casting line in this group. To achieve that maximum distance I need huge clearance behind me and simply can’t do it sitting down in a boat. Fishes shallow.
 

Conclusion
I ­­am now more convinced of the value of intermediate lines. I’d forgotten how much I enjoy fishing a slow intermediate just below the surface and how necessary a fast intermediate can be for taking flies to fishing depth and, from a boat, matching fishing depth to speed of drift and retrieve.

I have favourites from this group, but all the lines tested cast and fished well or well enough. For slow intermediate or neutral density lines, my choices are between the Barrio GT90 for distance and price, and the Snowbee XS ND as an easy casting all-rounder. Among the fast intermediates the choice is wider and more difficult, in the end I narrowed it down to the Hardy Mach or Rio Aqualux with the Vision Attack as solid budget-priced performer.