I recently heard someone mention that in order to control algae on ponds in this hot weather he completely "blacks out" his pond. He was talking to another person and I really wish I had interrupted and asked him what he actually uses to cover the pond. Does anyone know please?
I suspect that he meant he makes sure that the pond is well covered with plants like lilies that block out light and use up the nutrients in the water. If you blacked out the pond in terms of totally covering the water surface with something like plastic, a) it will look horrible, b) it won't do the fish or wildlife any good and c) it will kill the existing plants. Plant well to get around 2/3 of the water surface covered, also see the answers below.
That's what I would have thought Woofgang, but he was indicating with his arms like you do when you describe the size of a large sheet of something. Think I'll just get some more plants!
one of our ponds is fed by an underground stream which trickles in through a pipe then the overflow goes down an underground outlet pipe, via a well then into a very large pond. The little pond was prone to 'weeding up' but last year I threw a bunch of watercress in which colonised rapidly and controlled the algae brilliantly - when it gets too crowded the watercress is very easy to fish out.
The only time I've heard of someone using dye in water was the old quarry in leics where the owner wanted to stop people diving as it was dangerous, so he 'blacks out' the water with dye to stop visability. Might be the same thing but to stop the sun making the algae grow (?)