Fishing River Confluences

Embracing Confluences

River confluences are great places to fish for trout throughout the angling season. Zane Mirfin outlines some major opportunities associated with fishing confluences.

When I dipped the thermometer into the river and saw the numbers rocketing skyward, I knew we were in big trouble. The drought had taken a tight grip on the region, rivers were critically low, and the dry hills shimmering in the heat haze of the mid-day sun told a grim story to a couple of river-weary anglers. We fished a nice run more out of hope than any expectation, but it soon became obvious we’d need to seek cooler waters -- if we could find any. Racking my brain, I remembered a small tributary upriver, out of sight of the main road, which flowed from cool, heavily vegetated native bush.

The stream confluence offered immediate hope. The electronic thermometer gave an instant thumbs-up and, peering through long grass along the bank, I spotted several promising shapes in residence. Dick made an excellent first cast, a nice trout swung across the current, and slurped down his fly…

Water-body confluences can take a number of forms -- the meeting of streams and rivers, the entry of a stream or river into a lake delta, oxbows and backwaters, or even the confluence of a braided river into the saline waters of a coastal lagoon. This article concentrates on stream mouth confluence opportunities and potential fishing strategies, providing seven main reasons why confluences can be great places to fish throughout the angling year.

1) The first reason is nutrient enrichment. Many rivers in which trout live are a tough environment. Harsh flooding, scouring, low fertility, and acidity are just a few of the challenges fish face day-to-day. Acidity and alkalinity play a large part in the distribution of trout and food sources. I’m no fish scientist, but inflowing confluences I fish and guide regularly turn on rainbow trout in predominantly brown trout fisheries. Are the fish attracted to differing alkalinity input? I don’t know, but the fish sure look good thrashing in my net! Fertility is important because even bugs need something on which to live. Where there is food, there will be insects, crustaceans, and baitfish, which in turn become trout food. Many rivers are poor fisheries until a fertile tributary injects some life into sterile waters. Believe it or not, some rivers have become better because of intensive farming practices. As noted guide Tony Entwistle says: “Sometimes a little poo is good”. The Pelorus River, as an example, doesn’t become a good fishery until its smaller tributary, the Rai, injects some fertility and life into the harsh mineral-belt water. Tributary streams can flow from virtually any point of the compass and it is inevitable that some inject good and some inject bad water characteristics into larger waterways. The key is to have an understanding of the positive characteristics and their locations so you can exploit them. Knowing the good also means you know how to avoid the bad. I know rivers where you only want to fish above the confluence of certain tributaries.

2) Variety is another reason to target confluences, which are often extremely beautiful places regardless of success. It is no accident that many fishing beats are described in human terms by where confluences join. I can think of any number of helicopter day beats that go from one tributary point to another tributary upstream. Often when fishing parties run into each other, they divide the water according to confluences or inflowing streams. Confluences are a language anglers understand and embrace and will always be used as arbitrary stream markers and locations. They also give anglers additional fishing opportunities and can add excitement when deciding which stream to fish. Big or small? East or west? With the advent of didymo, though, ethics need to be carefully considered (see sidebar: Didymo Ethics and Hygiene).

3) Trout food concentrates where stable structure and water fertility is best. Most trout foods thrive under stable conditions, hence the importance of stable confluence water. You may find any aquatic trout foods from stoneflies to caddis in such areas. Food sources vary from region to region and sampling the food sources with a simple insect screen and kicking over a few rocks can give a valuable insight into how best to catch trout. Terrestrial foods can also be important seasonal foods, with everything from willow grubs, passion vine hoppers, brown beetles, and cicadas worth trying, especially on those fussy surface eaters. Seasonal food sources, such as inanga, smelt, mullet, and immature flounder, are common in areas of tidal interaction. Often an inflowing tributary makes a great area for ‘bait-balls’ of baitfish to accumulate. Confluences, such as the Mahinapua Creek with the Hokitika River on the South Island’s West Coast, are great hunting areas for predatory estuarine brownies. Small slim silvery spin lures, or ‘matuka’ style feather lures (Parsons’ Glory or Yellow Dorothy) fished on a sink tip flyline will seldom disappoint, especially during spring and summer. Female trout will accumulate in these food rich places to replenish body condition lost through the rigours of spawning. Fish at times of low light and on the falling tide for best results. Trout and salmon will often spawn in river confluences and spring outlets. If fishing these in late season/winter, don’t be shy to fish an egg fly or Globug where it is legal.

4) Water temperature is a critical factor in the feeding behaviour of trout. Entwistle has long documented the feeding behaviour of trout under thermometer scrutiny. Brown trout feed best in rising water temperatures between about 12-18C. Once the water tips over 20C, it is generally time to look for colder water because fish will shut down and go into survival mode. Rainbows will continue to feed in warmer water up to 21C, but most salmonids function best in colder water. Once water temperatures reach critical thresholds, it is irresponsible to continue catching and releasing trout in oxygen-starved waters. Exhausted trout in warm waters can be subject to high mortality. In-flowing tributary streams, springs, and rivers offer hope to anglers in such circumstances by introducing much needed colder water that assists trout feeding behaviour. Search out the optimum feeding temperatures. Small tributaries can often contribute the coldest water because they have shorter catchments and can have less land development and more native riparian vegetation cover. Some streams are often many degrees cooler than the main rivers due to complex geographical and geological features. Experience is important here and time spent in reconnaissance is never wasted. Always remember that the thermometer never lies. In the height of summer, the rule remains the same whether it is an inflowing stream on the Waikato or the Taieri: trout prefer cool waters. In colder periods of the year, water temperatures may be too cold for good fishing and warmer heavily developed tributaries may pump warmer water into a colder main river that will assist in concentrating feeding fish. Early season is another time to search out tributary inflows when water temperatures tend to be lower and the fish often sluggish.

5) Water clarity is a major consideration in trout feeding behaviour. In times of high flow and spate conditions, trout will often concentrate near inflowing confluences because clear water assists feeding vision and also allows them safety from mud-choking debris in a larger main river. Small tributaries mostly fall and clear faster than larger waters and offer sight-fishing opportunities in adverse conditions. Find clear water when everything else is high and flooded and you have a recipe conducive to catching trout. Some glacial-type rivers will be murky during spring and summer thaw, and clear inflowing confluences will attract trout like metal to a magnet. Likewise, the confluences of clear and tannin waterways are usually a sure bet to find trout. Often it is possible to find smaller tributaries or inflowing waters that are dirty/coloured/cloudy, while the main river remains clear. Fish are much easier to catch in cloudy water where they are more aggressive, less spooky, and generally hungrier. Fishing success can often be magnified by exploiting weaknesses in the salmonid defense system. Remember that clear water is not always best from a catching perspective.

6) The confluences of rivers often form magnificent trout pools. Hydrological and geomorphological processes can sculpt out magical pools that consistently hold and shelter more and bigger trout. One of the universal rules of trout fishing is to find stable structure where food, shelter, and general living conditions are optimum and fishing success will generally follow. Stable water is also much easier to fish, as there can be a better trout/water ratio. Fish the water carefully and thoroughly to find trout, regardless of method. All flyfishing methods will work at times throughout the angling year, as will spin and bait fishing. The key is to give the trout what they want to see, when they want to see it. If the water is clearer, use smaller food imitations and lighter line. If the water is bigger, coloured, or during late season preceding or during spawning time, you will often be able to use heavier line and larger more garish food imitations and attractors. Spin fishing with large lures during times of high flow or late season is a great way for junior anglers to get among the action. During high summer, trout may be willing victims to a large terrestrial dry fly, but playing it safe with smaller nymph rigs (often heavily weighted) can be the way to go. Don’t be disappointed if you can’t see trout in a feeding frenzy at a confluence. Be patient and watch carefully before you begin fishing. Once you have identified and located some prime locations, you can always return sometime when conditions or circumstances are better. Some confluences fish better early or late in the day. Some are impossible to fish in the late afternoon glare of the sun. The key lesson here is that they all vary and all confluences require a different approach. A prime skill of consistently successful anglers is being able to position themselves on prime water when conditions are optimal. If you know enough good water and locations, you will one day encounter environmental conditions that suit those places best and will be able to situate yourself to best advantage at the most favourable time, flow, colouration, temperature, whatever, and reap the rewards. Consistently catching trout is no accident, or matter of luck.

7) There are times of year when trout go loopy. Brown trout often go off the feed and are more interested in chasing one another in April – a prime time to fling a streamer on a sinking line. Rainbows will often concentrate at the mouth of an inflowing tributary prior to running up it to spawn. Often they may have to wait weeks for optimum flows to allow passage in a small tributary. During this time, they can be vulnerable. I have seen this behaviour with brown trout too, where often large numbers of fish will build up in a ‘staging pool’ prior to spawning. These pools often remain the same year after year and often are at the confluence of another stream or river. Such pools can fish consistently well in late season and are the bars and nightclubs of the fishy world, where singles meet spawning partners to travel together further upstream. Once you have identified places like this, it goes without saying that success is generally inevitable. Giving specific fishing advice for fishing confluences is difficult given the complexity and diversity of fishing opportunity within New Zealand. Rainbows can be more cooperative and less discerning than brownies, but the key is to always fish to the conditions. During spring and summer, feeding fish are likely to be taken on more conventional tackle and flies. During late season and winter, it may be more a case of stimulating the territorial aggression of the trout inhabitants with something big and flashy. The great thing about trout fishing is that there are few universal rules. So enjoy your time spent fishing confluences and marvel at what you can learn. Value and treat confluences with respect and care, as there is always something magical happening at the joining of the waters.

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Didymo Ethics and Hygiene

In the didymo age, ethics and hygiene are highly important for all New Zealand anglers. The diatom didymosphenia geminata is easily spread by careless individuals, who do not check, clean, dry. Knowingly taking didymo from one stream to another is a criminal offence. This can make the fishing of confluences tricky, if not impossible in some circumstances. Uncontaminated tributaries should not be walked with didymo-infected fishing equipment. To be safe, you should consider fishing only one waterway per day anyway. Fishing upstream or downstream, it is difficult to avoid not crossing tributaries and inflowing streams. It is probably ethical to cross such waterways to stay on your original river as long as you stay within the high water mark of the stream you are fishing. Walking upstream a few pools from your original river is a no-no in the didymo age!