In the last few weeks, a recurring question in the Extension office is about pond algae, pond water testing, and managing aquatic weeds. Algae and weed overgrowth is one of the most common problems for pond owners and can be unsightly at best and dangerous for fish and other animals at worst. If you have a pond algae or weed problem, there are a few things you should know.
Planktonic algae are single-celled, microscopic algae that only grow as deep as sunlight can penetrate the water and cause a green coloration in the pond. These algae are actually good algae, as they are the base of the pond’s food chain and produce oxygen for the water. Typically, planktonic algae are consumed by microscopic zooplankton, which are eaten by minnows, baitfish, and so on into the larger fish species. If your goal is to have a healthy fish population, managing and promoting planktonic algae is critical, and you want your pond to look somewhat dark and murky. On the other hand, if your goal is to have clear, pretty water, you should not expect to have much success fishing in that pond.
The second type of algae is filamentous, which as the name implies, is algae that forms visible chains, threads, and filaments. Typically, filamentous algae forms in the shallow bottoms of the pond, then floats to the surface to form mats across the ponds surface. Filamentous algae are unsightly to look at and cause the dissolved oxygen in the water to decrease, which can be harmful to fish. They also interfere with recreational activities like fishing and swimming- so they are a species that we want to manage when possible.
In addition to algae, there are a number of aquatic weeds that can cause problems for pond owners. Aquatic weeds are broken down into submerged, floating, and shoreline plants. Submerged plants root into the bottom of the pond, though some can break loose and survive floating in the water. They are often described as grass or moss. Floating plants have leaves that lay on the water surface, and may be rooted or free-floating. A common floating weed we get questions about is duckweed. Shoreline plants root in the shallow edges of the pond and may be vertically growing or more spreading in growth.
One of the most important pieces of managing your pond is learning to recognize what type of vegetation you’re having trouble with. Planktonic algae is beneficial- in most cases, we don’t want to get rid of it! Filamentous algae and weeds, on the other hand, need to be managed in order to maintain your ponds aesthetic and health. Identifying the algae or weed you’re having trouble with is the first step to deciding what management is required. If your pond has any nutrient runoff from pastures, hay fields, or even your garden- that likely contributes to the aquatic vegetation you have, and unless you solve the nutrient problem, you won’t solve the vegetation problem. Once you’ve identified the algae or weed, you can then look to biological, physical, and chemical control methods.
Control of aquatic weeds can be difficult. Sometimes, biological controls like introducing grass carp or other species that eat weeds and algae can be helpful. Physical control methods can include physically removing weeds and algae using a rake or deepening a pond that is too shallow and sunny. Ponds less than 18”-24” deep tend to have more weed and algae problems due to the penetration of sunlight to their bottom. Last but not least, chemical control is an option. A word of caution with chemical control is that you must have a correct ID of the algae or weed you’re trying to control, you must apply herbicides correctly according to label directions, and you must address the source of your overgrowth (most often nutrient runoff) for chemical control to be effective. If you need help managing your pond, please let us know at uge3181@uga.edu or 706-359-3233.
