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Fly Line is Critical for Trout Fly Fishing — Five Fly Line Densities Explained

Just learning how to fly fish for trout? Well then you probably have picked up a few trout fishing flies and you know that they are absolutely worthless when it comes to providing any weight when you cast them. Now if you have done other types of fishing like using trout fishing lures or trout fishing bait and this is your first experience with fly fishing, you might wonder how you are going to get that fly across the stream to the waiting trout. That is the function of the fly line (along with the rod and your casting technique). The fly line does all the distance work for you.

Fly line density is the technical term here. Density refers to whether the fly line will float or sink; and, if it sinks, how deep and how fast.

There are five densities available; the floating line, sink-tip line, intermediate sinking line, sinking line or fast-sinking line.


The floating line does precisely as named – it floats. Perceived as the easiest to cast and a mandatory first for beginning fly fishing anglers, the floating fly line is undoubtedly the most popular. This is the preferred line when fishing with dry flies; and is also used with streamers and nymphs. The goal of the fisherman using dry flies is to mimic an insect that is on the surface of the stream.

Streamers and nymphs are slightly heavier (you can choose your weight) and the weight of the fly pulls the line down slightly and returns the fly to the surface when retrieved. Again, this movement is designed to look like the aquatic food of the trout with its natural shape and movement and thus provokes a nice trout to “get his dinner”.


The sink-tip line is the second most popular as it combines both a floating and sinking line. The first 10-30 feet of line sink while the remainder of the fly will continue to float.

Nymphs and streamers are used with the sink-tip line as it takes these flies deeper but allows them to come easily to the surface when retrieved. The feeding depth of the trout may cause you to use this line as it will help you put the trout’s meal in his feeding zone.


An intermediate sinking line will sink completely but at a slower rate than a normal sinking line. This line is chosen when you want your fly to sink slowly. This is a very good line to use when the fish are at varying levels and you want your fly to look natural as it descends.


The sinking line descendes at a uniform rate fairly quickly. These lines can sink at a rate of two inches per second or as rapidly as ten inches per second. This line is used because you know the trout are feeding deep and you want to get down to them.


Finally, a fast sinking line sinks like a stone, as the name suggests. This line is also designed and manufactured to sink at varying faster rates. This is the line of choice when you want to get your fly really deep; really fast.


At this point, probably the only other thing to mention is the color of the fly line. You have already or will notice that fly line comes in a rainbow of colors.

Floating line color is a personal choice and you will see bright yellows and oranges being the predominant choices. If fish are deep, the water is dark and therefore sinking lines are also dark so they are not seen by the fish. The fish are less likely to see the darker line than a bright one.

If you are using a floating line you can select the color you feel is easiest for you to see. The reason for this is that the fish will notice the floating line, regardless of its color. On the end of the floating line you attach a clear line called a tippet. The tippet is usually around eight to ten feet in length. The fish will see the floating colored line but it will be too far away from the fly to cause concern.

Okay, enough talk about what and how; pick up your rod and reel; go get your line and flies and get out there and catch some trout. Here’s to you yelling “Fish On!”

Want to know more about trout fishing flies? Other great trout fishing essentials are found on our website..