The presence of large amounts of yeast can indicate a low pH, existance of fermentative conditions or severe phosphorous deficiency

Fungi are xtremely large, non-motile filaments (300-1000 µm). They can be straight, irregularly curved or bent filaments with true branching. Cells are very rectangular (3-8 x 5-15 µm) with very large trichomes and contain organelles and large intracellular granules and structures. A heavy cell wall is usually present. Cytoplasmic streaming may be observed. Fungi  are found mostly within the floc structure. The fungi staining is Gram negative and Neisser negative. No sulfur granules are usually present. There is usually no attached growth. No Sheath is present.  Spores and .

Most fungi have vegetative bodies called thallus or soma and are composed of one-cell-thick filaments called hyphae . These generally do not coalesce into a visible object, but instead form a microscopic network within the substrate, called the mycelium, through which food is absorbed. The more conspicuous parts of fungi like mushrooms are fruiting bodies, which are reproductive structures that produce spores.

Fungi may  reproduce asexually, for instance through the production of spores called conidia (Greek for dust), which form at the tips of specialized hyphae called conidiophores. In some fungi sexual reproduction has been lost, or is unknown.

Fungi can be similar to Cyanophaecae or large type 0041 although neither of these are branched.

Fungi and yeast are usually found in environments where there is a low pH. They are usually common in a biotower or a trickling filter. They can cause "plugging or ponding".

Low pH is usually the cause of fungi and yeast. pH can be increased on the influent or in the MLSS to above pH 6 and usually with a little bit of time they dissappear.

Fungi is often a cause of bulking. Too much fungi can cause an increase in polymer consumption and make dewatering harder.

Yeast can be similar to Tetrads

Yeasts can reproduce asexually through budding or sexually through the formation of ascospores. During asexual reproduction a new bud grows out of the parent yeast when the condition is right, then after the bud reaches an adult size, it separates from the parent yeast. Under low nutrient conditions, yeasts that are capapable of sexual reproduction will form ascospores. Yeasts that are not capable of going through the full sexual cycle are classified in the genus Candida.

Environment

Yeast physiology can be either obligately aerobic or facultatively fermentative. There is no known obligately anaerobic yeast. In the absence of oxygen, fermentative yeasts produce their energy by converting sugars into carbon dioxide and ethanol (alcohol). In brewing, the ethanol is used, while in baking the carbon dioxide raises the bread and the ethanol evaporates. Many food, dairy, breweries and wineries have yeast present in large amounts in the influent. Yeast can cause high levels of TSS and cause an increase in polymer usage to reduce TSS in final effluent if not controlled.