rock snot
Didymosphenia geminata (Lyngbye) M. Schmidt


Didymosphenia geminata is a freshwater, single cell, diatom (a type of algae) which attaches itself to a solid surface such as a rock with a stalk.It is light brown, brownish yellow, or white, looking very much like wet toilet paper. Didymosphenia geminata has the texture of wet wool or cotton, fibrous not slimy or slippery and is not easy to pull apart.
It can reproduce asexually, resulting in large mats. It is able to spread from a single drop of water containing the diatoms. It usually reproduces most readily in cooler temperatures but has been recently known to tolerant of warmer conditions.
Ecological Threat
Didymosphenia geminata can be found in a Found in rivers, streams, and lakes. Prefers flowing water sources. It blankets streams or lake beds; blocks plants from sunlight and animals that eat plants from reaching them; and greatly reduces dissolved oxygen content in water.


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EDDMapS Distribution

EDDMapS Distribution - This map is incomplete and is based only on current site and county level reports made by experts, herbaria, and literature. For more information, visit

State Regulated List

State Regulated List - This map identifies those states that list this species on their regulated list. For more information, visit

Taxonomic Rank

There is no applicable taxonomy of higher classification for this subject.

Synonyms and Other Names

Related Scientific Names:
Gomphonema geminata (Lyngb.) C. Agardh (Synonym)


Plants - Aquatic Plants