In the beginning of fly fishing, fly lines were hand made by utilizing various materials such as horsehair and silk. They were tied to the tops of fishing poles which prevented long casts or the ability to pay out line to a running fish.
In the 20th century fly rods and reels advanced and so did fly lines. Today there are many different types of fly lines designed to suit particular fishing conditions.
Regardless of the fact that the true nature of fly fishing lies with dry flies and floating lines, the greatest challenge to a fly fisherman comes when a heavy fly has to presented deep close to the bottom at a distance of 30m or more from shore.
As their name suggests, floating fly lines are meant to stay on the surface and never sink. They are designed primarily for targeting rising fish. However, a floating line is also good for fishing water up to 2m deep with a wet fly or nymph as only the leader and fly will sink. During a slow retrieve the fly will be moving up and down in a zigzag fashion. Some anglers use floating lines in combination with long leaders (up to 6m long), indicators and small fly patterns like chironomids. They let the flies sink and watch for the indicator, just like in float fishing. In light to moderate winds, the indicator will be riding on the waves, imparting a jigging motion to the fly below. This will entice trout to attack.
One of the great advantages of floating lines is, they do not make much splash on the surface and do not spook fish the way a sinking line does. To allow an angler fish reasonably deep while still presenting the fly with enough stealth, intermediate lines were designed. These are slow sinking lines (1-2in/second) that take time to get down to the bottom. The loss of time is usually well compensated by the improved catch. Intermediate lines allow an angler to fish at a predetermined depth; once the slow retrieve begins, the lines keep their position in the water column well. Both floating and intermediate lines are lightly colored lines and some are manufactured clear just like monofilament lines.
Unfortunately, quite often trout feed deep, outside the range of floating lines. This type of situation presents the ultimate challenge in fly fishing as flies are supposed to be weightless by design. A heavy fly attached to a floating line usually does not go very far and the properties of the line hinder its sinking. What a sinking line does is, it distributes the weight necessary to cast the fly and sink it, along its length. There is just one problem with that; sinking lines are difficult to pull out of the water. Usually an angler will have to strip most of the line back and then make a few false casts to aerialize it again. Sinking lines sink at rates of between 3 and 9 in per second but faster sinkers are possible. With sinking lines, heavier fly rods are necessary.
Fly lines are assigned classes from 1 to 15 based on their weight. For single hand rods, the class indicated on your rod should roughly match the class of your line. (e.g. #5 rod will work with lines between #4 and #6, but the loading length of line will be different). Apart from their ability to sink or not and their class, fly lines come in different styles (shapes) as well. The well known double taper (DT) line is good as a floating line while shooting heads (WF or SH) are good as both floating and sinking lines. The main difference between the line styles is the distribution of weight along their length, which dictates the style of casting or fishing (or vice versa).
A DT line is sually about 27m in length with tapers at both ends. It used to be the most commonly used line by fly anglers, but in the recent years preference has been given to the WF line.
This is a shooting line that has a few meters of heavier fly line (head) attached to uniform shooting line. WF lines are easier to cast in windy conditions and they can be used in combination with sinking tips to fish close to the bottom.
One thing to keep in mind with Spey rods is, the class indicated on the rod rarely matches the class of line the rod best works with. Usually one has to go with lines about 2 classes higher for Skagit style lines and about 1 class above for long belly lines.
These lines are considered to be the traditional spey lines as they are close to the original double taper design. A long belly line today has a head of over 17m (50 ft) and integrated running line of another 30m (90 ft). These lines are versatile but more difficult to cast. They do not handle sink tips and heavy flies well.
These lines originate in Scandinavia. Their heads are shorter than those of long-belly lines and are usually between 12 and 14m which accounts for pleasant casting. They are very suitable for smaller rivers and species that would come to the surface like Atlantic salmon and steelhead. Just as long belly lines, Scandinavian lines do not work well with heavy flies and sink tips. Some stripping is also required.
To get both far out and deep, the need for a new style of fly lines became evident. Fishing the big rivers of North America in late fall and winter requires a line that will bring a bulky fly down to a semi-lethargic steelhead or bull trout. Chinook salmon on the other hand do not rise to dry flies like atlantics do and are usually caught quite close to the bottom. The Skagit lines address all of these situations. They have a fairly short head of about 9m which is fished in combination with tips – sinking or floating. The sink tips are quite heavy and usually about 5m in length. This set up allows really big and heavy flies to be used and fished deep. Skagit lines are the easiest to cast and suitable to beginners. Although considered clunky, they have a lot of fans as they get the job done in the cold winter days when other fly fishing methods are doomed to fail.