Understanding Fly Line Sink Rates | Slow, Fast & I.P.S Explained

So if you’re not using the right sinking fly line then you’re not going to do as well as you could and this is never more true than over winter when we're hitting the big rivers, lakes and rivermouths in search of fresh fish.
A day on my local lake could see me slow pulsing nymphs, fast stripping a team of wet flies across shallow flats or plunging the depths across the drop offs to get to the harder to access fish.

A range of fly lines, and an understanding of their sink rates and applications, gives one a decided advantage.

Using Airflo sinking fly lines for hard to catch fish

Now let’s talk fly line specifics...


Airflo sinking lines are famous for their non stretch Power Core braid fly lines that let the angler feel exactly what the fly is doing, and every bump or pluck which occurs. Fly lines that stretch will absorb many of the takes that occur, especially when fishing a longer line. Bellies also occur when a line stretches, creating slack line, which also detracts from ones ability to feel the often-gentle pluck of still water fish.

I use Airflo non-stretch cores exclusively, and have noticed a vast improvement in my strike rate. Before this, I simply never knew the fish were there until it was too late. Some lines can stretch as much as 24%. Airflo Power Core reduces this to around 6%, a statistic which may not mean much now, but will once upon the water.


Density compensated fly lines are tapered to provide efficient energy transfer from the line down to the leader, and to ensure effective turnover. The forward taper thins down until the leader is reached. Of course, the thicker section of line in the middle known as the belly is significantly heavier. This results in the tip of the line, and hence your fly often sitting higher in the water column than the main body of the line, robbing you of precious depth.

Density compensated fly lines provide extra weight in the forward tip of the taper so that it sinks faster than the remainder of the line. If I buy a DI3 I want a DI3, not a fast sink with effectively an intermediate tip.


Airflo Sixth Sense Slow Intermediate Fly Line

Slow intermediates like the Airflo Sixth Sense fly line sink at around 0.5 inches per second (IPS) and are great for those calm, mirror-like days where line shadow and surface disturbance become a problem, and you don’t want to scrape along the bottom. They also fish well on windy days, where the breeze ends to blow floating lines around, dragging one flies.

Slow intermediates are great for retrieving damsel nymphs or double nymph combos across the shallows, and if called for, they will also float a dry for 20 odd seconds or so. Adding a fast sink Airflo Polyleader will allow you to fish across drop offs or down a little deeper when called for. In general, slow intermediates will play just beneath the surface.


Airflo Clear Camo Intermediate Fly Line

I use fast intermediates like the Airflo Clear Camo Intermediate, the Sixth Sense and 40+ for the majority of my stillwater fishing, and it’s a sink rate that is always close to hand. They are a comfortable line to use, and allow a controlled sink rate with a reasonably level angle of retrieve, great for when trout are chasing baitfish in the bays. By using a 2 or 3 fly team with a weighted fly on point, I can cover a range of depths on the retrieve.

Fast intermediates are my ‘go to’ line when employing ‘slow, slower, slowest’ retrieves with chironomid or snail patterns across weed beds where heavier lines would eventually get too deep and hook up on the bottom.

Airflo Polyleader Set

Airflo Polyleaders and weighted flies can be used in conjunction with your fast intermediate for that little extra depth where needed. Bear in mind, that the faster you plan to strip your retrieve, the closer to the surface you will pull your line. You may need to go to a faster sink rate if you need to strip deeper, and fast.


Airflo Sixth Sense DI3, DI5 & DI7 Sinking Lines

Airflo's Sixth Sense DI3, DI5 & DI7 fly lines are for getting down and finding the fish zone according to depth of the lake or the speed of the rip. The DI3 and DI5 will hold their own in the smaller rips where intermediates will often be held up in the water column, and are great for stripping blob flies or wee flashy wets quickly across the shallows. Fished from a boat, a reasonable angle of retrieve can also be achieved when wanting to get a little bit deeper with your three fly team.

The DI7 with a sink rate of around 7 inches per second is the big boy in my team and the next most often used for plunging the depths of our deeper lakes or for getting deep beneath the bigger rips. It's also great for swinging flies along the bottom of our heavier, deeper rivers such as the Clutha as well as many of the larger Canterbury waters. If you want a near vertical retrieve from your boat, or when drifting out the back of the rip, then the DI7 is the line for you.

Airflo 40+ Integrated Shooting Head Flyline

The Airflo 40+ DI7 has the advantage of floating running line, making for easier line management and shooting when wading the shoreline.

So don't hit the shoreline with your summertime floater and expect the best. Grab yourself the bargain Lamson Liquid 3 pack set, load a few different Airflo sinking lines up and find the fish all through the water column.


Chris Dore is a battle tested fly fishing guide with over 15 years of professional guiding experience, battling the demanding, ever changing conditions that our New Zealand rivers throw at us.

In 2006 Chris became one of the first New Zealanders to successfully pass the internationally recognised Federation of Fly Fishers Certified Casting Instructors examination and has since taught many thousands of anglers to up their skillset.

For more in person and on river fly fishing advice and upskilling why not book Chris for a day or three?

Winter lake fishing in Queenstown