Unsightly Lyngbya on Surface
Lyngbya is a problematic aquatic growth common to many ponds in North Texas. It is not an aquatic plant nor a true algae, but rather a blue-green cyanobacteria that can be a pond owner’s worst nightmare. It ranges in color and usually appears green, brown, gray, or black. It can be isolated to small areas of a pond or it can cover the entire surface in a dense mat. More often than not, it collects on the downwind side of a pond.
This bothersome growth is most common in the months of July, August, and September and infects approximately 15% of the ponds in the DFW area. The biggest problem with Lyngbya is that it is highly resistant to algaecides. There are a few products that can be used to manage the spread of Lyngbya; however, total eradication is virtually impossible without help from Mother Nature.
Lyngbya initially forms as a dense, carpet-like layer on the bottom of the pond. The cyanobacteria produce gases which then cause pieces of the mat to break loose and float to the surface. It is slimy to the touch due to the gelatinous coating it produces. This impermeable coating makes it resistant to typical algaecide applications. There are currently no products that have been proven to be 100% effective in penetrating this coating and completely killing the internal cells. Even when fragments are killed, the mucus-like layer prevents the Lyngbya from decomposing and sinking to the bottom. In this case, you end up with dead, white or gray colored remnants that continue to float on the pond surface for weeks at a time.
Discolored Lyngbya after algaecide application
The best way to manage the spread of Lyngbya is to change the conditions that favor its growth. Lyngbya thrives in shallow, clear water with elevated nutrients (phosphorus, nitrogen, and iron) and little or no water movement. Lyngbya is “iron loving” and thrives in ponds that are routinely filled with well water. Unlike most aquatic plants and algae, lyngbya can use atmospheric nitrogen as a fuel source. The growth will often migrate up and down the water column. Many times, the ponds will look great in the morning hours and then be covered on the surface in early evening.
The use of an approved pond colorant can be effective at controlling the spread. The dye will limit the amount of sunlight that penetrates the water column; thereby making it difficult for the Lyngbya to thrive. In ponds with low water movement, a surface fountain or aerator can be very beneficial. Reducing available nutrients in the pond with commercial binding agents is another option. And finally, routine algaecide applications can help keep the growth in check. But in the end, there is no simple solution for permanent removal. Unfortunately, lyngbya will never go away completely. As the water begins to cool during the fall, it sinks to the bottom where it will overwinter in the bottom sediment.