Control Algae Blooms in Ponds

What is Algae?

Algae exist in water bodies of all sizes. They can be carried to water by birds, land animals, boats, fishing gear, and even the air.

There are different types of algae that can be found in ponds, including filamentous, planktonic, and macroalgae. Filamentous algae grows at the bottom of the pond and can appear as green mossy mats, slime, or long hair-like strands. Planktonic algae float freely throughout the pond and can have different colors such as green, yellow, blue-green, or brown.

Macroalgae, such as Chara and Nitella, are often misclassified as submerged weeds but are actually forms of algae.

Managing algae blooms in ponds is crucial to prevent water imbalances and protect fish populations from potential harm. Algae require nutrients and sunlight to grow and proliferate. Controlling sunlight by using pond dye and reducing excess nutrients are effective management tools.

Filamentous

Pond owners commonly call filamentous algae string or hair algae. Growth begins at the bottom of the pond until it breaks free and floats to the surface in mats.

There are many species of filamentous algae so not all blooms will look the same.

String algae can look like green mossy mats, slime or long hair-like strands. The color of filamentous algae is normally bright green to dark green.

Pithophora is a type of filamentous algae that has a cotton-like consistency. Spirogyra feels like wet silky hair.

As string algae matures it eventually releases to the surface of the pond. Why does string algae float to the surface? It becomes buoyant from the oxygen it is producing.

Is string algae bad for a pond?

While filamentous algae may not be visibly appealing, it can provide some benefit to the pond when present in moderate amounts. It is a food source for invertebrates, protozoans, and fish.

If a bloom is covering the majority of the surface, this shows that excess nutrients are present. It is important to reduce nutrients levels within the pond or lake.

An algal bloom can create dangerous conditions for aquatic life in ponds and lakes. Algae produce oxygen through photosynthesis during daylight hours. They also consume oxygen 24 hours a day. At night, the algal bloom can exhaust the dissolved oxygen in the water and cause a fish kill.

Similarly, using an algaecide creates dead plant matter that consumes oxygen and can also cause a fish kill. Pond Aeration can reduce the stress on aquatic life and limit the risk of fish kills.

Planktonic

Pond managers commonly refer to planktonic algal blooms as green water or pea soup. These single-celled Diatoms float freely throughout the pond. Coloration of planktonic forms can be green, yellow, blue-green or brown.

Planktonic blooms can be a sign of a serious imbalance in water. If the visibility in to the water column is less than 18 inches, you should take steps to improve water conditions.

Planktonic blooms produce oxygen during the day and consume oxygen at night. A heavy planktonic bloom can result in a fish kill from oxygen uptake at night. These kills can also occur when there are consecutive overcast days. Without sun, planktonic blooms consume oxygen during the day instead of producing it.

Chara & Nitella

Chara and nitella are types of macro-algae. They are commonly misclassified as submerged weeds but are forms of algae. People also know Chara as muskgrass because of its strong odor.

Chara produces stems with leaves growing in whorls around the stems. There is a gritty calcified outer coating. Chara has a skunk-like odor. It is typically found in hard water.

Nitella has similar looking growth to chara but lacks the gritty calcified coating and has no odor. Nitella, typically found in acidic or soft water, is also more delicate than chara.

There is no root system with macroalgae forms.

Algae Control for Ponds

Effective controls for algal blooms include pond algaecides, pond dye, and beneficial bacteria to reduce excessive nutrients in the water.

Granular algaecides can be utilized to prevent and treat filamentous blooms by focusing on the growth at the bottom of the pond. After the mats have begun to float to the surface, liquid algaecides should be used to gain control.

Pond dye is an effective control when used consistently to block sunlight from reaching the pond bottom.

Reducing excess Nitrogen and Phosphorus in the water column is also a very effective preventative. Beneficial bacteria digest Ammonia, Nitrate, and Nitrite in the water and release it to the atmosphere as Nitrogen gas.