Not only is algae often a “catch-all” for all nuisance aquatic plants, it is often looked at unfavorably by pond owners, and for the most part, that would be accurate. Algae does play a critical role in your pond health, but an imbalance can be catastrophic to your fish population and overall pond health.
Benefits of Algae
Algae species, in general, serve a purpose and are essential for a healthy pond. Planktonic algae is the first link in most food chains that occur in your pond and your pond ecosystem needs algae to thrive. Zooplankton feed on planktonic algae and bait fish and fingerling sport fish in turn feed on the zooplankton. Without a food source, the bait fish and fingerlings will struggle and not thrive in your pond.
Often times, pond owners who are managing their pond for trophy bass production will fertilize their ponds to keep the planktonic algae population very high. This serves to provide more food for zooplankton, bait fish and fingerlings and also blocks much of the sunlight from reaching the bottom of the pond. In turn, other aquatic plants struggle which decreases the areas for bait fish to hide and gives the bass a much easier meal to come by. This can be effective, but also risky when managing against some of the harmful aspects of algae abundance.
Problems with Algae
Often the most frequent complaint about algae is aesthetics. A green pond covered with algae is unsightly and is an eye sore. The enjoyment of the pond or water feature is diminished when algae has taken over.
Algae poses a problem to your pond health when you have too much algae overall and during algae blooms. During the photosynthesis process when plants use sunlight and carbon dioxide to produce food, they give off oxygen. Photosynthesis is a good process for your pond. The plants are using carbon dioxide and giving off oxygen which is needed for your fish, decomposition of organic matter, and other processes within your pond.
However, photosynthesis only occurs when there is sunlight. As the sun goes down, plants turn from oxygen producing organisms to oxygen consuming organisms. Therefore, the more aquatic plants and algae you have in the pond or body of water, the more oxygen they will give off during the day and the more they will consume during the nighttime hours. As the night goes on, the oxygen levels continue to decrease. The lowest levels of oxygen will be just before sunlight in the morning prior to algae and plants producing oxygen again. If your pond has too much plant life, the oxygen levels can decrease to the point that large fish may struggle to survive.
An algae bloom is a rapid reproduction and spreading of algae when conditions are right. Algae blooms typically occur during the hot, sunny, calm part of the summer. When an algae bloom occurs, your pond can be covered with algae in a very short period of time. The major problem with an algae bloom is the eventual algae die off or crash. Often even quicker than the bloom itself, the algae die off can create major problems. A die off of an algae bloom can be caused by a cloudy day and lack of sunlight, a cold front, storms, cold rain, or even an over-aggressive chemical treatment in the pond.
When the algae bloom dies off, it adds a large amount of dead organic matter to your pond. This organic matter is decomposed by microorganisms at the pond bottom. With the added organic matter load on the pond, the total amount of decomposition occurring in the pond increases. This decomposition process often uses up oxygen and gives off carbon dioxide and even more harmful gases such as methane and sulfur compounds.
This causes two problems; the first is lack of oxygen. When the oxygen in the pond is used to decompose the dead algae, it is not available for fish and other aquatic life. A die off can be so severe that most of the available oxygen in a pond can be used up in the decomposition process and your fish and other aquatic life will start to die off. The larger the organism, the more oxygen it uses. Therefore, your larger fish that have been in your pond for several years will be the first to die when oxygen is taken up.
The second problem with a large die off and increased organic matter is nutrients. When the algae die off and are decomposed the carbon dioxide and nutrients are released back into the pond and is available for the next generation of plant material. The carbon dioxide and nutrients help to begin the cycle all over again.
In salt water or brackish water areas, Red Tide can occur. Red Tide is a naturally occurring phenomenon that can affect brackish and salt water areas and is a generic name for a harmful algae bloom. Among the thousands of algae species there are maybe 100 that produce toxins, which can be ingested by filter feeding shellfish. The right mix of ocean conditions including low salinity, high nutrient levels, warm water, and calm seas causes algae to grow rapidly. Red Tide often occurs when an extended period of sun follows an extended period of rain. Filter feeding mollusks such as clams, mussels, and oysters are not safe to eat when harvested in waters affected by Red Tide because the toxins can build up in these organisms. This build up is known as bioaccumulation, and over time, the more toxins an organism is exposed to, the more will accumulate in them, especially in bones and fatty tissues. When the organism is eaten, those toxins that have bioaccumulated are transferred to the organism or person eating it. Crustaceans such as crabs, lobsters, and shrimp as well as fin fish are safe to eat because they do not accumulate the toxins.
Excessive algae growth will also limit sunlight from penetrating your pond and can cause significant thermal stratification, which is temperature layers throughout the pond. The water that does not receive the sunlight and warmth will remain cooler and denser. This dense water sinks and oxygen levels decrease because it is not in contact with the air.
Another problem with excessive algae growth is with irrigation. Many golf courses, farmers, and home owners use ponds as a holding area for irrigation water. If the pond has excessive algae growth and is pumped for irrigation purposes, the algae can clog the pump and filters within the pump, adding many hours of labor to the project. The algae that passes through the pump will be distributed throughout the lawn or area irrigated and can be unsightly and leave foul odors as well.
Algae plays a vital role in any pond or lake environment. Without it, you would struggle to raise and maintain a healthy fish population. However, a pond can quickly come out of balance with an overabundance of algae and have several harmful side affects of this algae production. Regular monitoring and managing of the pond will ensure the best possible outcomes for algae.