How to Identify and Treat Pond Scum

Filamentous Algae: Filamentous algae, also called hair-like algae, usually attaches itself to the bottom of the pond’s floor and to rocks. When especially bad, filamentous algae breaks free and floats on the surface in the form of thick algae mats.

Chara: Chara grows on the bottom of the pond floor in large pillow formations. Chara is often mistaken for a weed although it lacks real roots and does not grow above the surface of the water. Chara has a musky odor and a crunchy texture.

Oscillatoria: Talk about pond scum! Oscillatoria is a form of filamentous commonly referred to as black or blue-green algae. It can also give your pond a red-purple tint. These may colors you want in your sunset… but not in your water.

Planktonic, or Microscopic, Algae: Planktonic algae can change the color of your pond water to pea soup green, brown, or red. Early detection is virtually impossible. Because these are such small organisms, the only way to know your pond is infected is to visually see that your water has changed color.

Large Leaf Pondweed: Large-leaf pondweeds have both floating and submersed leaves. Submersed leaves are large, oblong, wavy, and taper to the stem. Floating leaves are oval shaped. Parallel leaf veins are evident. Stems are seldom branched. Leaves alternate on the stem. Solid, tightly packed spikes at the tip of the weed rise above the water surface.

Coontail: The leaves of the Coontail whorl around the stem. They have a serrated appearance. Spacing between the leaf whorls is variable. Consequently, these weeds may be long and sparse or bushy. Near the end of the stem, the leaves and whorls are crowded. Branches fork repeatedly. Many people misidentify this weed as Chara.

Bladderwort: Bladderwort has finely divided leaves scattered along the stem. The leaves possess numerous bladder-like structures. Stems have many branches and are densely leafy at the tips. Flowers are yellow and rise above the surface.

Curly Leaf Pondweed:Curly leaf pondweed leaves are thin with wavy and finely serrated edges. Its stems branched. Upper leaves are often crispy and appear waxy. Leaves alternate along the stem. Flowers borne on spikes rise above the water’s surface.

Duckweed: Duckweed leaves are the size of a pencil eraser. The leaves appear individually or, upon closer observation, in clusters. Small root hairs hang down from the underside of the leaf. No stem is distinguishable. Heavy growth blankets the surface with a depth of many inches. Duckweed does not interconnect like Filamentous Algae. People often confuse this weed with algae.

Water Milfoil: Water Milfoil leaves are whorled in groups of four. Each leaf divides into many thread-like leaflets extending from a central rib. This plant forms tangled mats at the surface. Seed heads develop in mid to late season and may extend above the water surface. Treat when weeds are actively growing, but do so before flowering occurs.

Naiad:Plants of Naiad guadalupensis are rooted, submersed, and range from 0.1 to 1.0 m long. The leaves are usually opposite or sub-opposite, and range from 0.2 to 2.0 mm wide, and 0.3 to 3.3 cm long. The teeth along the leaf margin are small. There are 18 to 100 teeth per side and they are barely visible to the naked eye. Sheaths at the base of the leaf round to a slightly auriculate (ear) shape. The flowers are small, inconspicuous, and borne in the leaf axils on the same plant.