Excessive algae growth in lakes and ponds signals an imbalance in the aquatic ecosystem, causing cloudy water, foul odors, and reduced recreational appeal. This overgrowth threatens fish populations by causing fluctuations in dissolved oxygen levels. Sudden and harsh methods for algae removal often exacerbate this problem, leading to fish kills. Effective lake management employs removal and suppression strategies that prioritize the long-term health and safety of the entire aquatic community.
Understanding and Controlling Nutrient Sources
Excessive algae blooms are primarily caused by an overload of nutrients, particularly phosphorus and nitrogen, which act as fertilizer. Identifying and stopping these inputs is the single most effective, fish-safe strategy for long-term algae control. External sources include stormwater runoff carrying lawn fertilizers, pet waste, and decaying leaf litter from the surrounding watershed. Reducing these inputs prevents the problem from starting.
Phosphorus is also released from internal sources, specifically accumulated organic sediment at the bottom of the lake. This process, known as internal loading, occurs when low-oxygen conditions near the sediment cause bound phosphorus to dissolve and release back into the water column, fueling new blooms. Addressing this internal nutrient recycling is a complex but necessary step in restoration.
Establishing a vegetative buffer zone, or riparian area, around the shoreline is a preventative action. This strip of native plants helps intercept and filter out nutrients and sediment before they enter the lake. Studies show that taller grasses with strong root systems are most effective at sequestering excess nutrients, especially when the buffer is at least three meters wide. Removing accumulated organic debris, such as leaves and grass clippings, near the lake edge also minimizes the amount of material that can break down and release nutrients.
Mechanical Removal and Water Movement Solutions
Physical removal is a direct method for controlling existing algae mats without introducing chemicals that could harm fish. For surface-clinging or filamentous algae, techniques like skimming, raking, or netting manually remove the biomass. This process immediately reduces the amount of organic material that would otherwise decompose and consume dissolved oxygen.
Introducing water movement through aeration systems is a highly effective, fish-safe intervention. Aeration systems (diffused air or surface fountains) increase the concentration of dissolved oxygen (DO) throughout the water column. This elevated DO level is crucial for supporting a healthy fish population and preventing the formation of low-oxygen “dead zones.”
In deep lakes, aeration prevents thermal stratification (the layering of water with different temperatures and oxygen levels). By mixing the water layers, aeration ensures oxygen is distributed uniformly, reducing the likelihood of internal phosphorus release from the bottom sediment. The resulting oxygen-rich environment also inhibits the growth of certain types of toxic blue-green algae (cyanobacteria), which often thrive in stagnant, low-oxygen conditions.
Biological Methods for Long-Term Algae Suppression
Biological methods use natural processes to suppress algae growth, offering a sustainable approach. One common technique is biological augmentation, which involves introducing beneficial bacteria and enzymes. These microorganisms outcompete the algae by consuming the excess nitrogen and phosphorus, effectively starving the bloom.
Barley straw is another natural method that inhibits new algae growth (algistatic). As the straw decomposes in the water, it is believed to release compounds like oxidized polyphenolics and a trace amount of hydrogen peroxide. This release requires oxygen and time, typically taking between two and eight weeks to become fully effective.
In some jurisdictions, the controlled use of sterile grass carp (triploid grass carp) manages excessive aquatic plant growth. These fish are certified sterile to prevent uncontrolled reproduction and typically prefer to eat submerged weeds, though they will consume some filamentous algae. Stocking rates (ranging from 5 to 30 fish per surface acre depending on vegetation density) must be carefully determined by a fisheries biologist and often require a special permit.
Cautious Application of Chemical Treatments
Chemical treatments, or algicides, should always be considered a last resort due to the significant risk they pose to fish and other aquatic life. The primary danger following the application of an algicide is not the chemical itself, but the massive, rapid die-off of the algae. As this large amount of organic material decomposes, aerobic bacteria consume vast quantities of dissolved oxygen from the water.
This sudden oxygen depletion can quickly lead to hypoxia (critically low oxygen levels), which suffocates fish and causes large-scale fish kills. To mitigate this risk, calculate the water body’s volume accurately for proper dosing and treat only small sections at a time. Treating no more than one-quarter to one-half of the water body at once allows fish a refuge and the ecosystem a chance to recover.
Furthermore, any chemical treatment, such as common copper-based algicides, must be done in conjunction with continuous aeration. Operating an aeration system before and during treatment helps replenish the dissolved oxygen consumed by the decaying algae. This cautious, segmented approach minimizes biological oxygen demand and protects the fish population.