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Rivularia

Rivularia spp. · Algae

Rivularia: Where it grows

Where it grows · Photo: Heidi Meudt / CC BY

NativeColonial cyanobacteriaBlue-green (cyanobacteria)May produce toxins

Also called Hard algae balls, Blue green 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 Rivularia

  • Small, hard, dark green to brown hemispherical colonies on rocks and plants
  • Firm, sometimes crusty with lime
  • Pinhead to pea size
  • Fine radiating lines visible inside with a hand lens

Similar species

Gloeotrichia floats and is fuzzy; Chaetophora is soft jelly.

Growth profile

SeasonPresent much of the year, most visible in summer.
StartsAbout 55 to 60 F water
LightModerate to bright light
DepthAttached to rocks and plants in shallow water
How it spreads or reproducesFragments and resting cells
HabitatHard or alkaline ponds, lake shores, springs and streams, attached to rocks and plants.

Why it matters in a lake

Usually a minor part of the shoreline community. Common in hard water.

Where it is found

  • Idaho: Occasional
  • Oregon: Occasional
  • Wyoming: Occasional

Classification

KingdomBacteria
PhylumCyanobacteria
ClassCyanophyceae
OrderNostocales
FamilyRivulariaceae
Scientific nameRivularia spp.

More colonial cyanobacteria

GloeotrichiaStar jellyMare's eggsWarty nostocSpirogyraCladophora

Browse all algae in the Species Database

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We identify algae under the microscope and test for cyanotoxins, so you know what is in the water and whether it is safe.

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