Calothrix
Calothrix spp. · Algae
Where it grows · Photo: Peter de Lange / CC0
Also called Black crust, Calothrix spp., Blue green algae, Rock algae
May 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 Calothrix
- Dark brown to black velvety film or crust on rocks
- Often a dark band at or just above the waterline
- Firm, thin and hard to scrape off
- Tapering threads ending in fine hairs under a microscope
Similar species
Red crust alga is red and flat; Rivularia forms rounded colonies; brown diatom film is lighter brown and rubs off easily.
Growth profile
| Season | Present year round, most visible in late summer when water levels drop and bands are exposed. |
|---|---|
| Starts | Warm, bright conditions in summer |
| Light | Bright light and high sun |
| Depth | Waterline and splash zone to a few feet |
| How it spreads or reproduces | Fragments and short motile filaments |
| Habitat | Rocky lake shores, streams, springs and splash zones, often in hard or alkaline water. |
Why it matters in a lake
Forms the dark bathtub ring on rocks along many shorelines. It fixes nitrogen and is usually harmless.
Where it is found
- Idaho: Occasional
- Oregon: Occasional
- Wyoming: Occasional
Classification
| Kingdom | Bacteria |
|---|---|
| Phylum | Cyanobacteria |
| Class | Cyanophyceae |
| Order | Nostocales |
| Family | Rivulariaceae |
| Scientific name | Calothrix spp. |
More benthic cyanobacteria
Lyngbya
Oscillatoria
Phormidium
Scytonema
Tolypothrix
SpirogyraNeed a hand?
Worried about a bloom?
We identify algae under the microscope and test for cyanotoxins, so you know what is in the water and whether it is safe.
Idaho / Wyoming (208) 501-4531Oregon (541) 280-0596