In fly fishing, you cast the line, not the lure, so the fly line is arguably the most important part of the setup. The two decisions are simple: match the line weight to your rod, and choose the right sink rate for the depth and conditions you fish.
Match the weight
The first rule: a 9-weight rod takes a 9-weight line. The line weight is designed to load that rod. Get this right and casting is easy; get it wrong and the rod never loads properly.
Float, intermediate, or sink
- Floating line: stays on top. Best for topwater, dry flies, and fishing shallow flats where you want the fly high.
- Intermediate line: sinks slowly, staying just under the surface chop. This is the saltwater workhorse, it swims baitfish flies at the right depth for stripers and albies and cuts wind better than a floater.
- Sink-tip and full-sink: get you down fast in deep water, strong current and rips, essential when the fish are holding deep.
Build a small quiver
You do not need every line, but a couple of spare spools transform a setup. For a saltwater 9-weight, an intermediate for most days plus a floating spool for topwater and a sink-tip for deep rips covers almost everything.
Tip When the fishing is slow, change your line before your fly. Nine times out of ten the problem is depth, not pattern, so switching to a line that puts the fly where the fish are holding fixes more slow days than a new fly ever will.