Algae are a natural component of any farm pond ecosystem, but excessive growth leads to blooms. The two main types are planktonic algae, which are microscopic organisms that turn the water green or brown, and filamentous algae, which form slimy, hair-like mats often called pond scum. Overgrowth occurs when the pond is saturated with nutrients, primarily nitrogen and phosphorus, usually from fertilizer runoff, animal waste, or decaying organic matter, combined with warm temperatures and sunlight. Addressing an algae problem requires immediate cleanup, targeted intervention, and long-term management to restore balance.
Quick Fixes: Physical Algae Removal
Physical removal is the most direct way to immediately reduce filamentous algae mats. Using tools like a pond rake, specialized skimmer net, or a wire screen allows for the mechanical collection of the algae. This action offers an instant visual improvement and is particularly effective for controlling surface-clumping algae.
The removed material must be taken entirely away from the pond’s edge and surrounding watershed. If left on the bank, the decomposing algae will leach nutrients back into the water with rainfall, restarting the overgrowth cycle. This manual step physically removes accumulated nutrients from the ecosystem, making it a necessary measure while implementing more strategic controls. A pond vacuum can also be used for smaller areas or to remove settled debris and algae from the bottom, minimizing disturbance to the water column.
Using Chemical and Biological Controls
Intervention methods are often necessary to manage severe algae blooms. Chemical controls, known as algaecides, quickly kill the existing algae population. Copper-based compounds, such as copper sulfate, are common and effective against both filamentous and planktonic algae.
Applying chemical treatment requires careful calculation of the pond’s volume for safe dosage. Copper toxicity increases significantly as water alkalinity decreases, necessitating a water test to determine the appropriate concentration. A major risk is the sudden death of a large algae mass, which leads to rapid decomposition by bacteria that consume vast amounts of dissolved oxygen, potentially causing a fish kill. To mitigate this, treat only a portion of the pond at a time or use emergency aeration to boost oxygen levels.
Biological controls offer a slower, more natural approach by introducing organisms or substances that inhibit or consume the algae. Sterile grass carp are a common option, as these fish graze on aquatic vegetation, but their effectiveness can vary, as they sometimes prefer other aquatic plants over algae. Barley straw is another biological agent that releases compounds as it decomposes, inhibiting the growth of new algae cells.
The barley straw must be contained in netting and suspended in the upper three to four feet of the water column to remain oxygenated and effective. The straw’s effectiveness is not immediate, taking between one to eight weeks to become active depending on the water temperature, and it works by preventing new growth rather than killing existing algae. This method is environmentally compatible and is not known to harm fish or other non-target aquatic organisms.
Long-Term Pond Health and Prevention
The most sustainable way to manage algae is to address the underlying cause: an excess of nutrients in the pond environment. Nitrogen and phosphorus from sources like agricultural runoff, over-fertilized lawns, and septic systems fuel algae growth. Implementing a vegetative buffer zone, typically 10 to 20 feet wide, around the pond’s edge can significantly filter out these nutrients and sediments before they enter the water.
Controlling nutrient sources on the surrounding land is also necessary, including managing fertilizer use in the watershed and redirecting surface runoff. Introducing beneficial bacteria products accelerates the decomposition of organic matter, such as leaf litter and dead algae, locking up excess nutrients in the sediment and making them unavailable for algae growth.
Environmental adjustments, such as aeration and shading, make the pond less hospitable to algae. Aeration systems circulate water and increase dissolved oxygen, disrupting the stagnant, low-oxygen conditions that favor blooms. Circulation also prevents thermal stratification, distributing oxygen and promoting beneficial aerobic bacteria. Shading the pond using floating aquatic plants, like water lilies, or applying non-toxic pond dyes limits sunlight penetration, hindering algae growth.