Living with Didymo. A challenge or change ahead?
Graeme Hughes

It’s difficult to accept the condition of the Waitaki River now that didymo is well  established. It’s just as difficult to find the enthusiasm required to put a rod together to fish amongst the didymo.  An angling acquaintance said to me “That’s what fishing is all about. To be successful you have to fish to the conditions”. I suppose he’s right, but it is hard to erase those memories of just two years ago,  the river was clean and blue and fishing was almost stress free. We thought barring hydro tunnels and irrigation canals the river could only get better. How stupid was that?

There is a challenge to any fishing venture but today on the Waitaki the challenge is just so much greater. I can see that  threadline  fishing with spoons and wobblers in conditions I experienced last week would very soon raise the stress level until it no longer became possible to enjoy one self and I feel for the spin fisher. Last week, with the river a little higher than usual, the increase in velocity was sufficient to strip heavy growths of didymo from off the bed. where ever one looked there was didymo, moving, rolling downstream. Spin fishing would have been a nightmare.  We certainly picked the wrong day, perhaps the wrong river, but there aren’t many left!
 
Casting a nymph is an almost guaranteed way to catch a Waitaki trout. Fishing the nymph now takes on a new dimension. Prior to didymo a weighted nymph bouncing along the substrate  would  catch trout.  A long leader perhaps 3  or  4metres would solve depth estimation difficulties. Today however, the chances of completing a deepwater drift without picking up some didymo  is rare.  It is not so bad if  you can see and fish a short line to a feeding trout in the Waitaki,  but blind fishing deep runs is now a sure way to run into downstream drifting didymo.

Dry fly is almost fool proof  however if the fish are not feeding on the top then a lot of time can be wasted trying to get them to do so. 

Trout are still in the same locations they were before didymo,  they appear to be in similar numbers and on the now rare, clear gravel runs where didymo has trouble adhering to the smaller gravels, I assume because the water velocity keeps the substrate turning over, they are just as hard to make out, especially if the wind is ruffling the surface or the light is poor just like the good old days.

Sighting fish in the Waitaki can be all concentration however fishing amongst didymo is hard work. The eye of the hunter, or angler in this case, is always on the lookout for movement which will signal a trout feeding; a “wink” of a white mouth as a trout intercepts a food item, a swinging shadow on the substrate, the flash of a silver flank as a fish turns in a run. When didymo is in transit downstream, on the surface or suspended in the water column, there is considerable confusion as the eye detects colour, movement  and shadow  created by dislodged didymo.  All fish-like but all false alarms. And when a fish is hooked the leader and line may stay submerged  for a period of time, and as long as its underwater it will be catching didymo. Netted the trout will have acquired  several hundred grams of didymo, caught on the line and  leader some of which will accumulate around the head of the fish. Not a pretty sight .

The river bed looks a mess.  Stranded rolls of didymo lie along the shingle bars and  along the river edge. Above the water line dead didymo bakes in the sun to look and feel like papier mache. It hangs from overhanging branches and collects on submerged logs resembling woolly sheep carcases. The only thing missing is the smell,didymo is almost odourless.

Which brings me to a couple of  advantages fishing in  didymo, if one could or should  ever say that about didymo.  If trout are feeding over didymo , who knows what they’re feeding on, then they are easily seen, silhouetted against the light brown didymo covered substrate. So finding trout is easy even if you leave your “polaroids” at home,  The Waitaki is a big river and water speed and slippery or  loose substrate can make wading hazardous. Not  today. Wading on didymo is slip proof,  much like walking on carpet. Wading to a vantage point in fast water is now  a lot safer than before didymo.

There may be  things to learn when fishing in didymo infested water.  I noticed hand tied tapered leaders with several weights of line joined become good didymo catchers and prevent some of the fouled strands of didymo sliding down the line ruining the catching ability of your nymph. Wet fly or feathered lure fishing, not commonly practised on the Waitaki River would be inviting trouble and endless cleaning. I guess that if you needed to fish on the bottom, fly patterns tied and weighted to ensure the point and gape of the hook was on the top , the so called weedless patterns, would work best, however it does not solve the problem of didymo wrapping round your line.

If the trout population remains in the Waitaki River, and I can’t see how it can,  then I will need to get out there more and learn from experience on the water. My enthusiasm wanes,  and while I enjoy the individual feel of each of my fly rods their differing weights and actions with a number of well stocked  lakes only minutes away,  I could easily become a fisher of still water  using the same gear.  In the meantime I will persevere , and now that all the rivers around me are growing copious quantities of didymo, when I get sick of it as I’m sure I will, or the fishery fails, as I’m sure it must,  then I have the lakes to fall back on. Not as vibrant not as dynamic, but didymo free 

I read somewhere that most undesirable things that grow are cyclical by nature.  I fear that’s all we can hope for, an act of God, as I doubt if any  substance introduced by man will rid us of this prolific  freshwater invader.

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