Matching your sink tip to the prevailing water conditions can help you present your fly effectively to Steelhead like this. jeffbright.com photo
Sink tips are an integral part of a fly fisher's arsenal when presenting the fly to a Steelhead or Salmon, yet there are many misconeptions as to when you should fish them, how deep you need to be, and so forth. And, while Steelhead seem to break every rule in the book at times, these 5 general principles will usually serve you well on the river:
1) Consider the water temperatures, time of year and the fish you're searching for. During the Winter, Steelhead are often lethargic and most times won't aggressively chase down a fly unless it swings past their nose. This is particularly true for those fish that may have been in the river for a few months (exception: fresh, Winter run fish can be quite aggressive despite cold water temperatures). So, err on the heavy side when fishing sink tips in cold water, particularly in deeper pools and runs. Late Summer and Fall run fish can be very aggressive and willing to actively chase down a fly because of warmer water temperatures, so it's not necessary to fish deep in the water column. In this case, a Type 3 or a type 6 is usually all that's needed.
2) Make sure that you're not down too deep. If you have to unsnag your fly every other cast, your sink tip is too heavy for the water in front of you and will prevent you from fishing it effectively. The sink tip should touch the bottom every once in awhile to let you know you're in the zone, but not much more.
3) When not to use sink tips? When fishing small, clear coastal rivers in the Spring, heavy sink tips can often spook wary Steelhead. In this case, a long leader with a small, weighted fly that is cast well above the target area will help you avoid spooking finicky fish. Same goes for Winter fishing when river flows are at seasonal lows.
4) Bring a range of sink tips with you on fishing trips. You never know what to expect on the river and from pool to pool. A wide range of tips, including Type 3, Type 6, and varying lengths of T-14 and T-17 will enable you to cover a broad range of depths and currents. My personal favourite is the Descension Sink Tip system developed by Dustin Kovacvich and the other Nicholas Dean Lodge guides, which include varying lengths of lead core (LC-13).
5) Match your sink tip to the pool you're fishing. This might seem a rather obvious one, but many anglers will simply fish the same tip from pool to pool, regardless of the depths and current speeds. Each pool has its own seams, features, and current speeds, and keeping your fly in the strike zone requires a dynamic approach. If you feel that you're not getting down enough, go a little heavier. If you're getting snagged every other cast, lighten up.