Algae Overgrowth

Symptoms by part

Causes

• Excessive sunlight exposure in shallow water
• High levels of nitrogen or phosphorus from fertilizer runoff
• Poor water circulation or stagnant conditions
• Overcrowding of aquatic plants
• Accumulation of decaying organic matter like dead leaves

Could be confused with

• Cyanobacteria · Often called blue green algae, this forms a thick, mat like layer that smells earthy or swampy and feels like wet velvet, whereas true algae is usually stringy or slimy.
• Duckweed · Duckweed consists of tiny, distinct floating leaves with roots dangling underneath, while algae lacks any defined structure or individual leaves.

Treatment

1. Gently lift the affected plant and rinse the leaves and stems with a soft stream of clean water to dislodge the algae.
2. Use a fine mesh net to physically scoop out floating algae mats from the water surface.
3. Increase water movement by adding a small pump or fountain to break up stagnant areas.
4. Introduce floating plants like water hyacinth or water lettuce to shade the water and outcompete the algae for nutrients.

Without chemicals

• Manually remove algae with a rake or net
• Prune away heavily infested, decaying leaves to reduce nutrient load
• Increase the number of submerged oxygenating plants to balance the ecosystem
• Reduce the amount of direct sunlight by adding shade cloth over the water feature

Preventing it

• Avoid overfeeding fish if the plants are in a pond
• Use a pond liner or container that prevents soil runoff from entering the water
• Regularly remove dead plant debris before it sinks and decays
• Maintain a healthy balance of aquatic plants to consume available nutrients

When to act

Act as soon as you notice a green film forming on your plants to prevent it from blocking their photosynthesis. If the plant is completely smothered and showing signs of rot, remove it from the water to prevent further decay.

Questions people ask

Will algae kill my water lilies?

It rarely kills them outright, but it can weaken them significantly by blocking the sunlight they need to grow.

Is it safe to leave the algae in the water?

Small amounts are normal, but if it covers the entire surface or your plants, it will deplete oxygen levels and cause problems for the entire aquatic environment.

Plants it affects

• Corkscrew plant
• Giant Waterlily
• Sacred Lotus
• Waterwheel plant