Algae in the Caloosahatchee:

Summer 2005

Microcystis aeruginosa

In mid August, people began noticing one of the biggest blooms of a microscopic organism many

have ever seen in the Caloosahatchee.  Bright green ribbons of masses of this organism, which is

commonly called blue-green algae, now streak the river for over 20 miles from near the Franklin Locks to the mouth of the river.  Microcystis aeruginosa can produce a toxin that can kill fish, irritate people's skin and, on rare occasions, cause nausea and vomiting.

The South Florida Water Management District (SFWMD) has prepared a primer on blue green algae -- you may read it by clicking here.  The SFWMD also provides information about its sampling program on this site.

State and local agencies began monitoring the bloom the week of August 15th.  Here's what we know about the blooms so far:

The most dominant species is Microcystis aeruginosa - a blue-green algae (also known as cyanobacteria) that can produce toxin (but does not always do so).  It tends to bloom in late summer (this is the same species that is blooming in the St. Lucie estuary).

Species which are present in lower numbers include

• Glenodinium, a brown algae,

• Dinoflagellate, which can produce toxin but does not always do so,

• Chlamydomonas, a flagellate not known to produce toxin,

• Phacus, a flagellate algae which does not produce toxin, and

• Cylindrospermopsis raciborskii, a blue-green algae (also known as cyanobacteria), which can produce toxin but does not always do so.

Flagellates and dinoflagellates are motile algae, whereas cyanobacterial varieties are non-motile. 

Results from tests on samples taken by the SFWMD at six sites in the Caloosahatchee on August 22^nd showed toxin levels between 1.51 and 7 parts per billion.  On September 6^th, toxin levels ranged from .44 to 7.45 parts per billion, and on September 19^th the toxin levels in the river ranged from 1.41 to 28.8 parts per billion.  The World Health Organization (WHO) considers any sample above 1 part per billion unsafe for drinking.   WHO standards for recreational boating waters consist of a range: 

• relatively low risk of adverse effects: 4 ug/L microcystin

• moderate probability of adverse effects: 20 ug/L microcystin

• high probability of adverse effects: scums

The Florida Department of Health encourages people to not participate in recreational activities or drink water from an obvious algal bloom.  Small children and pets are at greater risk because they are more likely to consume water while swimming so extra supervision is suggested.

Aerial Photos by John Cassani

Land Photos by Susan Brookman and Brenda Brooks Solveson

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Last modified: Monday July 13, 2009.

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