Aphanizomenon

Aphanizomenon spp. · Phytoplankton

Under the microscope · Photo: CC0

NativePlanktonic cyanobacteria (in the water)Can produce toxins

Also called AFA, Grass clippings algae, Aphanizomenon flos aquae

Can produce toxins

Only a lab test shows whether a bloom is toxic. Keep people, pets and livestock out of discolored or scummy water until it is tested.

How to identify Aphanizomenon

Under the microscope: straight filaments bundled side by side into flakes or rafts
Long cylindrical cells, with heterocysts and long akinetes partway along the filament and narrowed, colorless end cells
In the water: blue green flakes that look like floating grass clippings or pine needles
Blooms can turn whole lakes cloudy green and make blue green scums

Similar species

Dolichospermum filaments are beadlike and do not bundle into flakes; Planktothrix filaments are single, never bundled, and lack heterocysts.

Profile

Season	Can start in late spring and peak midsummer to fall; can even bloom in cool water.
Starts	About 55 to 60 F and warmer
Light	Full sun; floats with gas vesicles
Depth	Upper water column and surface
How it spreads or reproduces	Filament fragmentation and akinetes in the sediment
Habitat	Lakes and reservoirs with high phosphorus, especially large shallow lakes such as Upper Klamath Lake and many irrigation reservoirs.

Why it matters in a lake

Fixes its own nitrogen. Some strains make anatoxin a, saxitoxin and cylindrospermopsin, although the Aphanizomenon flos aquae that dominates Upper Klamath Lake usually tests low; blooms crash suddenly and can cause low oxygen fish kills.