A month ago I was sorting out a tangle at the tip of my rod, and when II clipped the last bit off, my rod butt and reel went 'gloomp!' into Lakenvlei dam.
After some dithering I dropped the anchor to mark what I thought was the spot and because the water was so clear and I could see the bottom, tried to find it. Not realising the water was so deep I was looking for something the size of a reel, when I should have been looking for something the size of a bottle cap.
Once I saw how small the anchor looked I realised my mistake.
The next day I tried again but was hampered by low light and a choppy surface.
Being of Scottish descent, there was no way I was going to let this go and buy a new rod and reel, so tied a coke bottle to a rock to make a temporary bouy.
Three weeks later I was back with my scuba gear, and it wasn't long before I found it. Also in the same area was a broken oar, but no treasure. It was still in good condition, but oddly the tip of the line and leader were missing. Crab?
Two others who had heard of my plans asked me to search for lost anchors at the point opposite the pump house where they had both lost one.
Getting my 'support boat' to tow me over was a bit of a joke, so I swam there.
Oddly the water was much murkier, and once I got below 12m was much colder (So there is your target depth in the summer months). At 15m it was quite dark, and even if I had a torch, I wasn't going to go deeper. No anchors were to be seen, and having plenty of air I explored the shallow areas.
The 'green' area with plant life extended to about 7m on average. This is the area which would have damsel and dragonfly nymphs, as well as crabs. There was no evidence of crabs deeper than the 'green' zone.
Below that the zone where effective sunlight did not reach, the only evidence of life was midges, and lots of them.
Perhaps you could use this info for your fly choice.
Closer to the hut inlet, where I was earlier and the water was clearer, the green zone extended to about 10 -12m, and the area looked so much more fertile.
Besides spending 3- 40 minutes underwater, I did not see one fish.
They probably fled to the other side of the dam when they saw this strange creature.
Midge habitat in Lakenvlei dam