The Biggest Rainbow Trout in the World – Tekapo Canal, New Zealand

The hogs that gave hog city its name.

You’ve seen ‘em on Instagram. You’ve wondered what Photoshop wizardry was involved. And then you’ve realized they’re real. Gerhard Uys looks at how nature and unique growing conditions conspire to create the 20lb-30lb rainbow trout in the hydro canals of the New Zealand South Island.

@nzyoshi letting a 24-pound rainbow go.

What and Where is the Tekapo Canal? 

The Tekapo Canal is part of the Waitaki hydro electricity scheme on New Zealand’s South Island. It is a network of lakes and canals that feed glacial water to eight power stations.

Photo from

The scheme was initiated in the early 1900s when existing power generators could not provide enough for the New Zealand South Island. It now provides electricity to well over 800,000 average New Zealand households. With a population of only about 5 million people in entire New Zealand and the most staying in the North Island, this is massive.

According to a 2014/15 National Angler Survey (NAS) this network of lakes and canals is collectively the most popular freshwater sports fishery in New Zealand. The popularity of this fishery has exploded in the past 15 years, with a over a 16- fold increase in angler use measured between 1994/1995 and 2014/2015. A  study showed that between June to October 2019 there were over 4000 recorded angler days on the Tekapo Canal alone. The Tekapo Canal is where most of the monsters are caught, and it draws a quarter of all canal activity during winter season, according to the NAS survey.

The Monster Rainbow Trout:

The canals connecting the lakes sets the scene for the growth of massive fish. 

As the water is glacier fed and ultra-clean, salmon farms cages now line the canals. According to New Zealand farmed over 14,000 tons of King salmon (Chinook) in 2018 with almost 5000 tons exported to over 20 countries. 

The primary reason for the large trout is that excess feed from salmon cages sift into the canals and large schools of wild trout simply hang around and gorge themselves on this feed.

@tom_hodge_safaris with a wide canal rainbow.

A recent report by The National Institute of Water and Atmospheric Research found that it is not just excess food that finds its way through salmon cages into the canal that leads to such large specimens, but also the prevalence of native prey fish and snails as a food source.

According to Ben Boothy, who guides almost exclusively on the canals, there are other factors that contribute to the excessive sizes of canal fish, even if they don’t feed near salmon cages.

“A client of mine caught a 23lb rainbow. Its stomach was packed full of freshwater snails. There’s a massive population of freshwater snails in the canals. One snail is about the size of half a thumb,” Ben says.

Whether it’s eating snails or excess food from the salmon farm, the trout and occasional salmon in the canal are supercharged.

“I find that anything that has a constant food source is always fully charged up. You will get a wee two to three pounder on the line and it will put up a huge fight. These fish have balls! Because of the constant food source these fish are almost in the same condition than other fish are in when they prepare for spawning. In other places, this only happens at a certain time of year, but here it is constant. ,” Ben says.

“There’s a certain population that lives around the cages and grows fat. However, there’s also a population that doesn’t live anywhere near the cages and are still really big. I believe it’s because the canal system has created a tailwater type fishery. The lakes in the area all drain into the canals. This channels a constant source of food from the lakes to the canal connections, and fish simply sit below these sections and hoover up food. There are big populations at the top of canals that never move from the tailwater and they are large. I have found pods of over 100 fish in some areas,” Ben says.

Fish feeding in different areas will vary in size and look.

“Fish that feed close to salmon cages may look like fat ‘blubberballs’, but big rainbow or browns that feed near dam inlets may be 25lb and look like a backcountry fish. 

There are also big brown trout in these canal systems. Photo: Ben Boothy. 

Fly Fishing Techiques at Tekapo Canal:

According to Ben, “As the canals can be as deep as 36ft and 196ft at its’ widest, fishing it isn’t easy. (The canals are long. With Tekapo Canal alone stretching for about 16 miles).”

“The trick is getting flies down as fish sit at the bottom of the canal to get out of the current. The water velocity is fast and a 3gm or 6mm tungsten nymph is key, there’s no way around it. I would rather use a heavy nymph than split shot,” Ben says.

Ben recommends a setup with a massive bomb on the sharp end of the line plus an egg, creeper or worm fly.

However one can also use a single egg.

“A dropper type system can create problems as some fish are so large that any second hook often attaches itself to a fishes’ body when you are fighting it. Lines and hooks then snap during a fight as angles of lines then become ‘all wrong’.

Hannah Clement @shes_on_the_fly with a beauty.

“Using one egg limits things that can go wrong,” Ben says.

Focusing on areas where lakes feed into canals is the most sure way to catch fish on the fly  as that is where fish congregate for food sources.

“Focusing on these areas meant we have had massive success. Just prospecting along the canal isn’t as efficient,” he says.

With the canal depths and speed fluctuating drastically between times of high and low electricity needs, one’s approach needs to be adjusted to conditions.

“With low flow, there is more ‘access’ to fish, but because they see so much gear (especially spin gear) they are so much harder to catch.  I like high flow, it gives fishless time to think and they just react and eat”.

Hannah Clement @shes_on_the_fly with a beauty.

The Czech Nymphing Approach: 

In deeper sections a traditional fly approach can be effective, with a long 20ft leader and a massive indicator. In rocky sections where water is 9ft deep and very fast a Czech Nymphing approach may be better.

He recommends a heavyweight rod, as a light rod will extend a fight and hampers the chances of fish surviving. 

“Because the canal is mostly uniform we cast upstream and drift/walk down.”

Ben says one of the biggest mistakes he sees when someone tries to land a fish is when they get lead feet.

“People stand still while they are trying to pull a fish. With a 25lb rainbow it’s impossible. You should fast walk down the canal while you fight. Like when chasing Tarpon or anything big, try and pull the head towards the tail and you will win.”

With the depth of the canals, sight fishing is not practical.

“If you are sight fishing it means you are catching fish off the edges, which means you are probably pulling them off their spawning redds. Such fish are already tired and need to be brought in hard and fast, and released, otherwise you will often see them drifting belly up a few seconds after being released”. 

Yoshi Nagawa’s Fly Fishing Techniques:

Yoshi Nagawa, Auckland based photographer and fly fishing guide says with talk of so many fishermen using spinning in the canals he needed to find out if fly fishing is possible there. Yoshi Czech Nymphs most of the time and believes this is also effective in the canals.

@nzyoshi showing off a beast of a canal rainbow.

“The canals are no different from normal rivers. You just have to adjust your mentality when you are there and find the right sections to fish,” Yoshi says. 

“Look for bends in the canal where you can see a current line. Target that. Any structure is also good, even a weed bed, fish will congregate there. Where lakes flow into the canals are also good. I don’t think in times of low flow it is effective to fish as you cannot get the fly moving. ” he says.

Yoshi fished edges where it isn’t too deep.

“Target areas where the canals are no deeper than 6ft – 9ft. This means you can easily stay in contact with the bottom on Czech Nymph.

He says the takes in the canal are really subtle with no real ‘bang’, and he believes Czech Nymphing is ideal as one can feel the take and stay in contact with the bottom. 

“I suggest a tap tap tap (on the bottom) and lift. If you are not hitting bottom you are not fishing.”

He suggests an eye drop sinker or split shot that will get the fly down to the bottom where fish lie. He then uses either a natural and an egg, or two eggs. 

“It is important is to get the flies away from the sinker or split shot.”

“A sinker or split shot on the bottom is actually quite noisy and fish seem to get annoyed by it. I also snapped my leader a few times when the fly was too close to the sinker. The first fly needs to be at least 3ft from the sinker/split shot, and the second fly at least 1ft away from the first fly. You could do hair and copper and an egg for example, but the water is somewhat murky and I don’t think the type of fly makes such a difference. Especially in the winter season spawning fish are very opportunistic and if they can see it they will eat it”.

Yoshi suggests a 6wt or 7wt 10ft rod. He managed to land a 24lb trout on a 5wt but says it was real ‘shitty’.

“One doesn’t have control with smaller rods. Once fish take off and go to the other side of the canal you are screwed. They just sit at the bottom and you cannot get them up. For a tippet a 6lb or maybe 8lb is fine. For an expert a 6lb tippet is fine. The water is very mirky so fish won’t see the line”

Nymphing any deeper than 10ft means line management becomes difficult, Yoshi says.

“Short to medium casts work. With too ‘long cast it’s a struggle to keep the line up.”

Spin fisherman walk down the canals with the current but Kyoshi says he would mostly stay put in one place, cast a few times, and then move on and repeat.

“The next thing I want to do is hit it in summer and sight fish with dry flies,” Yoshi says.

It’s a common misconception that the canals are for wintertime fishing only. 

Photo: @nzyoshi

When to Fish the Canals:

“The best fishing is early in January when there are warmer temperatures.” 

Ben believes early mornings are the best time to fish the canals. 

“It’s all driven by the electricity requirements. In the morning when everyone is getting out of bed you’ll find the toaster and kettle getting turned on, and at about 7:30 am the canal speeds up. The faster the water the better it is to fish. Fish have less time to think.”

Photo: Kiyoshi Nakagawa @nzyoshi

Regulations on the Tekapo Canal:

As of late the Tekapo Canal is open year-round, except for closure of spawning areas. Bag limit is 4 sportfish. Only two can be trout. All salmon must be over 11 inches long and only two salmon may be larger than 19 inches.

The scheme is not without some controversy. After the 2019 study, the CSI will close the upper half of the Tekapo Canal Fishery between 1 June to 31 August 2021. (Besides this closure the canals are open year-round). This is after concerns that fishing in the canals is not sustainable because of the large number of anglers. 

Accommodations and Travel:

When it comes to accommodation when fishing the canal you have two one-horse towns to choose from. Twizel and Lake Tekapo. Lake Tekapo is closest but may be fully booked in season. Twizel is a 40 minute drive away. Both towns offer access to backcountry fly fishing, hiking and hunting. Queenstown airport is the closest airport. Have a look at road conditions for winter as it can snow heavily. I have had the most luck with AirBnB, as opposed to motel accommodation.

Article from Gerhard Uys be sure to follow along with his adventures at @lets_hope_the_weather_holds

Photos from Kiyoshi Nakagawa who hails from Japan but resides in Auckland, New Zealand these days. He is a professional fly fishing guide and photographer. Give him a follow at @nzyoshi.

Be sure to check out Ben Booty online as well at and on Instagram at @boothys_fishing_school_ltd

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