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Freshwater vs. Saltwater Fly Lines

How do you determine weights for freshwater vs. saltwater fly lines?

Many avid freshwater fly fishermen are also occasional saltwater fly fishermen and, I am quite certain that the reverse is also true.

As an avid follower of one aspect or another of this fantastic sport, you quickly become aware that the gear used for each type of fly fishing is drastically different from the other.

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Fly rods are designated both by the total length of the rod and the line weight it was designed to cast. But, while many freshwater fly fishermen instinctively know exactly what length rod and what line weight they need for any given situation, determining the equivalent saltwater rod is not instinctive by any means. I am certain that the same is true for a saltwater fly fishermen trying to choose a freshwater fly rod.

Thus, you would think that somewhere on the vast reaches of the World Wide Web, there would be an article somewhere that matches freshwater fly line weight with the corresponding saltwater fly line weight.

After months of searching, I was unable to find anything that shared this valuable information, so I set out to do the research myself in order to answer this elusive question. After several more weeks of assembling disparate pieces of information, I finally found all of the pieces to the puzzle!

The reason that this question is so critical is that unlike other types of fishing, where you depend on the weight of the lure to bend or “load” the rod, when fly fishing, your lure actually has relatively little weight and quite a bit of wind resistance.

Therefore, in order to cast such a lure, you have to use a weighted line instead and, of course, the larger and more wind resistant the fly is, the heavier the line you will need to cast it.

One of my first clues to unlocking this mystery was that I noted that nearly every fly rod manufacturer on the market today offers freshwater rods in line weights ranging from 1 to 6 weights and they offer saltwater rods in line weights ranging from 6 to 14.

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Then, I recall running across a post on a saltwater fly fishing forum on this subject where a fellow stated that he used a 10 wt. for everything (which sounded an awful lot like a 5 wt. or 6 wt. to me). Then, I was looking at an Angler’s Workshop rod building catalog, at the St. Croix fly rod blanks in particular, when I saw the final piece of the puzzle.

By combining these three key pieces of information with some more supporting facts, I was FINALLY able to make the following equations:

Freshwater Fly Line Size = Saltwater Fly Line Size

2 wt. = 6 wt.

3 wt. = 7 wt.

4 wt. = 8 wt. 

5 wt. = 9 wt. 

6 wt. = 10 wt.

If your experience agrees with or differs from mine, or if you know of another article that either supports or disagrees with my assessment, then please feel free to post your comments below.

Freshwater vs. Saltwater Fly Lines