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Red Algae Spotted in Dyersville
July 30, 2021

Why is this water red?

Reid Stamer, Impact7G Stream Restoration Ecologist, noticed a strange phenomenon on a recent inspection of a newly established oxbow in Dyersville, Iowa. The bright red coloration is likely due to the presence of red euglena (Euglena sanguinea). Red euglena is a freshwater alga that can overpopulate the surface of a water body if conditions are adequate. High temperatures, coupled with excessive sunshine and nutrients, generate a pigment known as astaxanthin, which gives the algae its reddish color. Red pigmentation protects the algae from prolonged exposure to sunlight.

Astaxanthin is indicator that the water body is stressed. However, the presence of red euglena in an oxbow (where the coloration was discovered) can be considered a benefit to the larger stream system and watershed. Oxbows are natural separations from the meander of a stream, either naturally or by design. Confining red euglena to an oxbow allows for organic pollutants to be broken down and filtered without traditional water treatment systems.

Red euglena does produce a compound that is toxic to small fish. It is not known to be a danger to other wildlife or humans except in very large quantities. Avoiding water pollution from domestic wastewater and animal waste can help prevent conditions where the algae can thrive.

Photo Credit: Reid Stamer, Stream Restoration Ecologist, Impact7G

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