Trout running up Lake Taupo tributaries like the Tongariro during winter have only one thing in mind. They are heading to the upper reaches to spawn. These trout are not actively feeding and hug the bottom on their journey upstream. While they may move a distance sideways to intercept your fly, they won't come up for it. So when you are nymphing Taupo rivers during winter you need to ensure your flies are getting down to the trout.
The higher your flies drift above or away from the trout the lower your chances are of catching them. A fly dragging along the bottom gathering algae or mud with a tungsten bead clanging on the rocks is also unlikely to get eaten. Ideally, your fly needs to be drifting just above the bottom, right in the trout's face. So how do you achieve that?
It's actually surprisingly difficult to reach the perfect depth on every drift and it's probably the number one problem most anglers have that prevents them from consistently catching trout during winter. Aside from how heavy your flies are, there are many factors that influence the speed with which your flies will sink (sink rate) and how deep they will get. So let's break them down. Many of these factors will be obvious, but bear with me. In the end, I will give you the basic starting points I use for my indicator nymphing rig and how to adjust the rig and weight of the flies to get to the right depth. It's just good to refresh your memory and think about these factors when you are on the water. That will help you figure out what you need to adjust if you are not catching fish.
1. Depth of the water
Now this one is pretty obvious. The deeper the water is the longer your fly is going to take to get to the bottom and the longer your leader will need to be for your fly to reach the correct depth.
2. Flow rate
Again pretty obvious. More water moving faster gives your fly less time to get down during your drift.
3. Currents
Rivers don't have laminar flow. There is always a mix of currents both vertically and across the river. The more complex these currents are the more they affect how your fly will drift and sink. Back eddies and big swirling currents often push your flies back to the surface or out towards the bank and can really mess up a drift, while currents of different speeds cause drag on the surface and below.
4. Leader length
When you are nymphing with an indicator a longer leader often results in less drag and a better sink rate, but can make casting a nightmare, especially with added weight. There is also the fact that your fly can't go any deeper than the length of your leader. The basic rule of thumb for leader length is 1.5 x the maximum depth you plan to fish.
5. Leader thickness
A thick section of 0x (12lb) or a tapered leader will sink slower and be more affected by currents than a thin level 3x (+-8lb) leader will. Unfortunately, thin, level leaders are more difficult to cast and can have a tendency to tangle more. So it may be a balance between what you can comfortably cast and how thin you can go.
6. Size and material of your fly or flies
Perdigons with their tungsten bead and smooth epoxy body are made to sink fast and will sink faster than a buggy hare and copper of the same size. Now add a trailing size 10 globug and that rig will sink a lot slower.
7. Distance of your drift
A long drift gives your flies more time to get down to the right depth and more time at that depth. That's why it's often easier to fish big, slow and deep pools than a short, fast deep pool. It can be a real challenge on a river like the Hinemaiaia to get your flies down quick enough in the fast water with pools that are often small but surprisingly deep.
8. Your ability to mend
Good mending counteracts drag and aids your flies in getting down. It's vitally important to master this skill as it won't matter how heavy your flies are if you don't mend well. Without mending, drag will kick in very quickly and your flies will drift unnaturally, won't sink and sometimes they will even be pulled to the surface.
9. Weight of your fly or flies
Yes, I did not forget this bit. We all know that the weight of your fly will have the biggest influence on how fast it sinks and how deep it will get. How heavy your fly should be is the title of the post, so let's get to that.
How I set up my nymphing rigs in winter for Taupo rivers
My standard indicator nymphing rig when fly fishing Taupo rivers in winter consists of 12-14 feet of level 3x (+-8lb) fluorocarbon or nylon tippet material that goes from the fly line to a 4mm or 4.6mm tungsten beaded fly, like a hare and copper or a pink beaded caddis pattern. From the bend of the hook of the heavy fly, I attach another foot of 3x or 4x tippet to an egg pattern or small natural like an otter's soft egg, globug or size 14 flashback pheasant tail. My indicator is a sliding NZ strike indicator and I adjust the size to the weight of the flies and the river conditions. I slide the indicator down if I am fishing shallow and up to the fly line if I am fishing deep.
If the river I plan to fish is low and clear I will opt for the 4mm bead, a 14-foot leader and possibly a natural over an egg pattern. The slightly longer leader helps with the clear water and to get the lighter fly down while still being manageable to cast. If the wind picks up or I need to go heavier for some reason and struggle to cast the rig, I simply shorten the leader by 1 to 2 feet. It's amazing how much difference the leader length makes to casting. If I am fishing a smaller fast river like the Hinemaiaia, which isn't as deep, but where I need to fish heavier to get down quicker I might even shorten it to 9 feet. That helps with casting in tight spots while still being long enough to get down in the deeper pools on that river.
Leader length and weight are a balance. If you can't cast a long leader and heavy fly you are better off changing it up and seeking out shallow, smaller or slower water where you can effectively fish with a rig you can cast. If your flies aren't in the water and down at the fish's level you won't be catching anything anyway.
With the 4mm bead rig, I may well be too light for most of the big deep pools or fast runs on the likes of the Tongariro. So I always carry split-shot in sizes BB (0.4g) and AAA (0.8g). In a deep pool or fast run on the Tongariro, I will generally add a BB split shot to my rig without thinking twice and I may even lengthen my leader if it has become short due to bust-offs or fly changes. I prefer adding weight that I can remove when I fish in shallow water than having to change to a light fly. However, if the river is high or I only plan to fish fast or deep water I might just start with a 4.6mm bead fly and not bother changing anything. A 4.6mm bead plus a BB split shot are pretty much at the edge of my casting ability anyway, and I am more likely to hurt myself than fish effectively.
That brings me to an alternative to using heavy flies. Split shot is allowed, so why not simply use split shot instead? Honestly, I often do that now, especially on snaggy rivers like the Hinemaiaia. It's easy to use either a single fly with a split shot above a triple surgeon's knot or leave the tag on the triple surgeon's knot and fish two unweighted flies. You can easily have a flashback pheasant tail and an egg pattern to cover both options while adding and removing a split shot as needed based on where you are fishing. This is where the BB and AAA split shot is very handy. You can mix and match it as needed for any depth you need to fish. BB (0.4g) is roughly the same weight as a 4mm tungsten bead and AAA (0.8g) is roughly the same as 4.6mm tungsten bead. If you are concerned about lead, there are lead-free options like Loon's black drops.
How do I know if my flies are deep enough?
This is a somewhat tough question because a lot of it is based on experience, but here are some key ways to tell if your flies are reaching the right depth.
The best way to tell if you are deep enough (apart from consistently catching trout) is to watch what your indicator is doing. When your heavy fly touches the bottom regularly your indicator will start to "tick", dipping or stopping ever so slightly as the heavy fly bumps along the bottom. You want this to happen toward the middle or end of every drift without the indicator being dragged under. This means that for a large part of the drift, your flies will be in the strike zone.
If your indicator is doing this "ticking" seconds after you cast upstream or is being dragged under frequently during the drift then you are most likely too deep. It's still better than too shallow but flies dragging on the bottom aren't ideal either. The only other time your indicator may get dragged under is in strong currents and fast water where the indicator can be pulled under without the flies hitting the bottom or a fish grabbing them. In that case, you may just need a bigger indicator or put on some more floatant.
If you are getting "perfect" drifts with no "ticking", no dipping of the indicator and no snagging then you are probably not catching fish either. That is a clear sign you are not getting down and something needs to change. Consider all the factors I mentioned above to work out which part of the rig needs the change, make the change and then try again until you get it right.
I truly hope this article has been useful for you. If it has, please share it with someone that may also find it useful. If you want to learn more about fly fishing Taupo rivers in winter have a look at the video below, there is plenty more I can teach you.