by Michael Embrey, Partner & Biologist, Managed Wildlife & Fisheries LLC
Moss, scum, algae … beginning in early spring and running throughout our growing season I receive numerous calls regarding this unsightly pest. From small farm ponds to large trophy fisheries, it seems that few are able to avoid the plague of algae as warm temperatures and sun filled skies arrive in East Texas.
Understanding the root cause of algae and how to handle it can be tricky and typically leads to years of frustration as it keeps reappearing. By using several different approaches, one can reduce and at times eliminate this problem that most pond owners will experience.
Filamentous algae is a single-celled organism that thrives in aquatic environments with an excess nutrient load. It is typically noticed after it has filled with gases and floats to the surface forming large mats, but its life typically begins at the bottom of a pond or lake. This stringy mat is commonly referred to as “moss” or “pond scum” and floats in large green masses causing difficulty for fishing and navigation. At times, algae can even lead to decreased oxygen levels and fish kills if it becomes heavily established. First, let’s explore what causes algae to form in the first place.
East Texas is prime for algae growth. Long, hot summer days, nutrient runoff from fertilizer or livestock waste, and shallow clear water are all ingredients that fuel an algae bloom. Typically when I am called to a pond with a significant amount of algae there are a few things I observe. The first is a source of nutrients, either from agricultural or residential fertilization nearby, or from livestock. As fertilizers are applied in the watershed, runoff drives these nutrients into the water where they mix into the water column, fueling algae growth. Areas where livestock are present in relatively high numbers end up with the same result. Nutrient rich manure washed into the pond after heavy rain is the equivalent of adding fertilizer, further accelerating algae growth. Second, there is usually either a large area of shallow water (less than 3’), or the water is relatively clear. This allows sunlight to penetrate deep into the water column and reach the floor, providing the source of photosynthesis needed for algae to establish and thrive. Understanding the root causes of an algae bloom are important when you are attempting to find a solution. If you don’t address the cause of the problem, you will fight the battle for years to come!
Now that we understand what causes algae to establish, what can be done to treat it? Beginning with the root causes, it is likely difficult to keep livestock away (especially if this is their water source) or stop fertilizing hay pastures and residential lawns. It is likely that algae will be a recurring yearly problem in these situations, but there are ways to reduce the overall nutrient load. Recently there has been success using phosphorous reducing products to help bind the nutrients and essentially “lock them away” where they cannot be utilized by nuisance vegetation and algae. While I don’t endorse any specific companies, there are several choices available to pond and lake managers that do not require any special licenses or permitting. These products are typically applied to the water by either broadcasting them or through application via sprayer. My experience with these products has been positive, and they are a good solution to begin to remedy the source of the problem. There are other products available in bag form that can be used if there is a specific area that you can identify as a source of excess nutrients, such as a creek or ditch leading to the pond. In this case, bags can be placed in these areas and as water flows through them, phosphorus is stripped from the water and contained within the bag, keeping it from ever reaching the water body.
As previously stated, most algae will form in shallow, relatively clear water. This is difficult to fix in an established pond, but should be considered if you are thinking about building a new pond or lake. Having shallow areas for spawning ground is a necessity if the pond is used primarily for fishing, however, if you can construct the pond where the majority of the perimeter at the water’s edge drops off quickly you can create a scenario where it is difficult for algae to develop. Instead of gradually transitioning depths from 1’-3’, it would be beneficial to reach 3+’ of depth in as short of a span as possible. This reduces the surface area of shallow water where sunlight easily reaches the pond floor and can make a significant difference in the amount of nuisance vegetation and algae that is able to form.
So what do we do when this all sounds great, but you have an algae problem that needs to be fixed now? I use a multi-faceted approach, using both algaecide and biological control options. Algaecides are typically copper-based and come in liquid and granular formulations. Unfortunately, I find that pond managers often purchase one of these types of algaecides without knowing that they are used for separate scenarios. Granular algaecides are typically most effective at the beginning of the growing season when algae is starting to form at the bottom of the pond. These granules sink to the bottom and treat right where algae is forming, without doing much for the rest of the water column. This is a great way to get ahead, but should be thought of more as a pre-emergent than a solution when algae has already established. This is best used along the perimeter and around docks early in the growing season. As always, read the label and use the labeled rate when using these products, as fish toxicity can occur at excessive rates.
Liquid copper-based algaecides are typically more successful when treating algae that has already begun to surface and form mats. These products are diluted with water and sprayed onto the surface, where they penetrate the algal mats and begin to kill the algae. This is relatively easy to do with a sprayer, but a boat may be needed in areas where there is algae that cannot be reached from the shoreline. With my herbicide spray boat, I am able to treat algae and vegetation at the surface level, and also inject algaecide subsurface to reach algae that is still at the bottom. This is typically something that is not easily achieved by most lake owners, but should be considered as surface applied algaecides typically do not treat the algae still growing beneath the surface. Care should be taken to treat no more than roughly 1/3 of the surface area of the lake, as decomposition can lead to significantly reduced oxygen levels and a fish kill. If fish are a concern, follow the label instructions, but I typically advise to treat about 1/3 of the lake and then follow up by treating the next third 2 weeks later, and so on.
For those who have concerns about using algaecides, or who want to provide as many treatment options as necessary to control algae growth, the stocking of tilapia can lead to good results. In my experience, stocking tilapia at a rate of 15-20 pounds per acre will typically provide reasonable control of algae if it is not heavily established. Tilapia provide the benefit of consuming algae and providing a food source for predator species large enough to consume them, typically being largemouth bass. The downside to tilapia is they will not survive the winter, even in East Texas. When water temperatures dip below 50-60 degrees, tilapia will die and are consumed by bass and other predators. Unfortunately, tilapia must be stocked every year.
From experience, the best way to significantly reduce algae problems is to utilize as many of these treatment options as possible. For most of my lake management clients I begin by addressing any excess nutrients with the products I referred to earlier. By reducing excess nutrients, you can reduce the amount of “fuel” available for algae to thrive. After this problem is addressed, I typically stock tilapia and begin spot-treating any algae that has been observed. By using this type of approach, further treatments throughout the year are usually low cost “spot treatments” instead of having the spray a significant amount of algaecide several times throughout the year. Notice that I haven’t yet promoted using a pond dye as a way to control algae. Pond dyes are typically applied more to achieve a certain aesthetic than they are to control algae and vegetation. These products are often advertised as “preventing algae” or “reducing algae”, but truthfully, I haven’t seen them make any significant impact. I rarely utilize pond dyes, and they are typically for a small backyard pond type setting for aesthetics more than vegetation control. The better alternative to reducing water clarity is to promote a plankton bloom via lake fertilizer. HOWEVER, if you have any established algae or vegetation, this will add fuel to the fire and cause the problem to get out of hand in a hurry. This is best done in the future, at the beginning of growing season, and after all other nuisance vegetation and algae has been significantly reduced using the other methods previously outlined. A properly fertilized pond can produce significantly more fish than an unfertilized pond, but it is best handled by a professional, as there can be detrimental effects if not done properly.
No matter if you call it moss, scum, or algae, I feel your pain as someone who fights it on a weekly basis from March through October. Unfortunately, this is typically a long-term battle instead of a quick solution, but I hope that you were able to take away some valuable tools from this article that help you in the future. Managed Wildlife & Fisheries offers full-service pond and lake management if you would like professional assistance. From vegetation treatment to electrofishing surveys and fish stocking, I am in the field weekly assisting landowners achieve the pond or lake of their dreams. You can reach me at www.managedlands.com or at michael@managedlands.com for assistance.
