A blue-green algae bloom on the Lake Okeechobee side of the Port Mayaca Lock and Dam in western Martin County is more than three times too toxic to touch.

The bloom contained the toxin microcystin at a level of 29 parts per billion, the Florida Department of Environmental Protection reported on its algae website Monday morning.

That's more than three times the 8 parts per billion the federal Environmental Protection Agency considers hazardous in recreational contact.

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The 50-by-100-yard bloom was within the "wing walls" of the lock with "streaks of BGA (blue-green algae) throughout this area upstream of the structure," according to a South Florida Water Management District crew that reported the algae Wednesday.

No algae blooms have been reported in the C-44 Canal downstream of the dam. The canal leads to the St. Lucie River.

The gates at both the Port Mayaca dam at Lake O and the St. Lucie Lock and Dam, where the C-44 empties into the river, have been mostly closed since Lake O discharges ended March 30.

The St. Lucie dam gates have been opened periodically to release buildups of rainfall runoff from the canal.

Lake O discharges to the St. Lucie are unlikely in the near future. The lake elevation Monday was about 11 feet 4 inches, nearly two feet lower than the average for July 1.

But the locks at both sites open and close for boats on a regular basis With a bloom on the lake side of the lock at Port Mayaca, some algae could move from the lake into the canal.

More:C-44 Canal fish have toxins, OK to eat occasionally, ORCA says

Fluctuating bloom

The size and toxicity of the bloom at the dam has waxed and waned since it was initially reported June 5, but this is the first time it's been significantly toxic.

The first report described the bloom as having "no visible boundaries," and a water sample taken at the time contained microcystin at a level of 1.48 parts per billion.

A second check June 12 reported the bloom had grown to "200 yards in each direction" but had gotten less toxic: 1.08 parts per billion of microcystin.

The bloom was gone when a water management district crew visited the site June 20.

Microcystin can cause nausea and vomiting if ingested, and rashes and hay fever symptoms if touched or inhaled. The toxin also has been linked to long-term, sometimes fatal, liver disease.

Some scientists believe another toxin in blue-green algae, known as BMAA, can trigger neurological diseases.

Much higher toxicity was reported last week further to the south at Canal Point in northwestern Palm Beach County.

More: With toxic algae bloom in Lake O, Audubon scientist says don't eat fish

A bloom on the lake side of the structure leading to the L-10 Canal, aka the West Palm Beach Canal, contained microcystin at a level of 58.5 parts per billion, more than 7 times the EPA threshold for being too hazardous to touch.