Didymo finds its way into the Otematata River.
Graeme Hughes.
 
Didymo should be of extreme interest to all river users. After  a considerable period of colonisation, first brought to my attention on the 21st January 2006,  a black day for any Waitaki angler, it has prospered with an especially good growth rate during the months of the last winter. Just last week Didymo was  detected in the lower Otematata River tributary of Lake Aviemore, which is probably not surprising located in the same catchment as other infected waters. It is noticeable however that in the Waitaki River along with the Haka and the Maerewhenua Rivers didymo appears to be dying off in places. There are increasing numbers of Waitaki River users who report similarly.

I had an interesting Email from a friend, a local fishing guide, who passed on the following observations.

“During the past few weeks I have managed to get out and about on the river and have seen some surprising 'things' regarding that damn Didymo. I know I have mentioned some time ago that I believed that the Didymo appeared to be dying with some areas of river bed now completely clear, just typical river bottom as one would expect prior to this invasion.
 
Last Saturday afternoon, I had the opportunity to go for a flick down the river and  the biggest (one of the biggest) changes I noticed was the fact that the area just below the old Haka mouth (where the stop bank is), used to be well covered (understatement) in Didymo. The length of the Didymo seemed to be 'quite long' but was hard to actually determine due to the depth of water. However, on this recent outing, the same area has changed quite dramatically in my opinion. There are of course obvious patches in this area covered with Didymo (alive or dead?) but generally, there has been a massive 'clean out'.
 
Further down the river in one area, I came across a patch of what I would describe as 'budding Didymo', small dark areas where it usually first becomes noticeable when alive and doing well. When in this stage, I have the opinion that it was bloody hard to remove from the rocks. Again, here was a difference. This apparently 'budding Didymo' which would normally be hard to remove, just scraped away with ease with a wipe of my boot.
 
I state this VERY cautiously but I am almost convinced that this crap is 'on the way out'.  Of course, there are plenty of areas where the stuff is still quite obvious but again, it all seems to be disappearing, dying and certainly not increasing.
 
Water temperatures have been 'warm' but I have not done any actual temperature readings/recordings but I do wonder, would the water temperature over recent months, have played a part in the reduction (my opinion) of the Didymo ?”.

Any bad news for didymo is good news  and only time will tell. While it is early days yet there are plans to study, in depth, no pun intended, the spring fed groundwater streams which didymo has failed to colonise. It will be very interesting.

With Pukaki water colouring the upper lakes, which should filter down through the valley, didymo could be in for a rough winter. As didymo prefers maximum sunlight the glacial sediment in the water may reduce sunlight penetration and didymo does not enjoy a shaded substrate. Glacial till in the Waitaki River was always an annual event however over the last few years the river has remained clear throughout the winter. While I have not worked out why this occurs, it could be ice and snow conditions on the main divide, climatic changes or power generation, or a mix of these; if it its bad for didymo then long may it last.
I long to see the Waitaki Riverbed clean and grey again, something that many of us took for granted.

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