Pond Boss Forums INTRO Questions & Observations Black Algae

Hello to all,
Yesterday I found our pond had floating black algae in it. It looks awful. If you try to break up these clumps they crumble into small pieces. We do have a skimmer on the pond outlet which is actually the overflow pipe which collects it and drains into the creek bed. We never had this kind of algae before. I do not use any chemicals at all in the pond. We are going to aerate with our neighbors windmill and hopefully this will help with the "stringy type algae" too. Perhaps we should chemically treat this black algae before it spreads, or maybe it is all over the bottom of the pond already? Our pond is about 60 x 80 ft, with sides that gradually slope in. It is about 15 ft at its deepest point. We recently put in about 55 bluegills which are now spawning and 2 bass which are about 8"long. This is the first time we have put fish in our pond, as it was recently redug ( last August ) I presume they eat the creek chubs as there population has diminished drastically. They too have spawned in the pond. There are numerous pollywogs also, and a couple of painted turtles. All of the above seem to be doing fine so I suppose the water chemistry must be ok. Thanks Kay

Eeesh. Sounds like the pond is taking in too many nutrients for the small system to cleanse itself.

We see this kind of thing from time to time. An aerator system usually does the trick, using sunlight and oxygen to "burn" up the nutrients before they have a chance to feed the algae.

Mark McDonald
Editor, Pond Boss

Microscopic Picture My guess is that your pond contains a specie of Lyngbya (which is a genus of multicellular filamentous algae that are commonly found in a wide variety of habitats).
If correct, I really can't suggest a chemical control measure. I've had customers trying everything (legal) but the kitchen sink, but to no avail.
Based on the size of your pond, your best option may be to invest in a quality aeration system and/or try a good nutrient-reducing bacteria treatment program.
Good luck.
KD

Kay - Kellie is partially correct about the algae being Lyngbya however it could also be Oscillatoria the two are closely related (Blue-green, Cyanophyta) and quite resistant to chemicals. Both can form blackish spongy mats especially on mud bottoms (epipelic - growing on mud). This type of algae can frequently be seen on the bottom of mud puddles when the sediment has lost its oxygen. My experience w/ it in ponds is that it basically develops after the sediments have turned black underneath. Disrupt or rake your sediment where this stuff is growing is it blackish?
Mark is not correct about an aerator "burning" up nutrients. There is no scientific research that has proven that an aerator can do this ie physically dissipate, dissolve, burn, or blow off into the air nutrients. This is especially true for ammonia (nitrogen type nutrient NH4 & ions).. Ammonia can not be air stripped from the water UNLESS the pH is ABOVE 12. Numerous papers (authors) say you can blow off ammonia with aeration but this is a myth. If this was true fish haulers would not have any trouble with ammonia build up in their tanks. I've always suspected that heavy aeration can help bind soluable phosphorus (ortho-phosphorus) in the water column but I never seen any proof or scientific research that it works. BASICALLY, ONLY PLANTS ABSORB NUTRIENTS FROM THE WATER. To my knowledge there are no large economical nutrient vacuum cleaners for large ponds except water plants. Aquarium filtration techniques can strip some nutrients from the water on a small scale.
A good aerator that produces a STRONG boil may? help you get rid of your "black algae". A windmill aerator probably won't do much; too weak of a boil, low currents, little spread of the water. Dragging a rake (like a Lake Rake on a rope) or disrupting the bottom and sediments will probably do MORE to reduce the problem than anything else you can do. Nature usu. does it in lakes with strong wave action. An aerator will definately improve your water quality!