Scientific Anglers Sonar Sink 25 Coldwater Fly Line

When you need to get streamers deep and fast in coldwater conditions, Scientific Anglers' Sonar Sink 25 Coldwater is the go-to line. Built around a compact 25-foot extra-fast-sinking head, this line delivers the weight and control you need to reach fish holding low in the column without sacrificing castability or handling when getting there. It’s a purpose-built sinker for anglers who aren’t afraid to throw heavy flies in big water, and it's an especially popular choice for those looking to throw massive articulated streamers at true predatory giants--from the post-spawn brown trout bite in the middle of winter to figure-eighting your way into a springtime musky eat that'll be stained in your brain for the next ten years, this line tackles all of your predatory needs.

Features

SA Line ID — SA's Line ID provides markings in the first 1–2 feet of the tip for instant at-a-glance identification of line model and grain weight — handy when you’re swapping heads on the boat or rigging up in low light.

AST (Advanced Shooting Technology) — AST is SA’s dry-slick coating that sheds grime and reduces guide friction for cleaner, farther shooting. On the Sink 25 this means better turnover and longer, crisper casts even when pushing heavy streamers and sinkheads.

Welded Loops — Strong, low-profile factory welded loops on both ends for fast leader and backing attachment, smoother turnover, and reduced splash on pickups — a small detail that improves hookup chances when big fish bite deep.

SONAR Sinking Technology — Proprietary, fast-sinking tungsten and density formulations that drive flies downward and keep them there. In the Sink 25 this tech creates an extra-fast 25' sinking head that gets streamers into the strike zone quickly and efficiently.

Uses
Streamers SA's Sonar Sink 25 Coldwater line is made for streamer enthusiasts targeting bass, trout, steelhead, pike, musky, salmon, stripers, and more. It’s ideal when you need to get big flies deep fast, whether you’re swinging across current seams, stripping through a reservoir, or probing the depths of a cold river.

Temp
Cold to Moderate Engineered specifically for coldwater applications (but still comfortable in moderate temps), the Sink 25 maintains low memory and predictable sink performance when air and water temperatures drop. This line is not intended for tropical/warmwater use, however.

Taper/Weight

More Mass Towards the Front of the Head - The Sink 25 Line features a short, aggressive 25-foot sinking head followed by a substantial handling section. This taper is built for efficient turnover of heavy streamers and weighted flies, with grain weight offerings clearly marked to match the perfect line to your setup with ease. An excellent choice when fishing fast-action rods and when throwing large air-resistant flies to predatory fish.

More Info

Best For: Trout, Salmon, Steelhead, Pike, Musky, Bass

Loops: Front Loop (Leader to Fly Line Connection) and Back Loop (Backing to Fly Line Connection)

Sinking/Floating: 25' Sink Tip (sink 3 and sink 6 option)

Other Resources

2020 Tropical Saltwater Fly Line Shootout & Buyer's Guide

Fly Line Temps: Tropical vs. Coldwater

Freshwater Fly Line Shootout & Buyer's Guide