Ecologists continue to monitor Herrick Lake near Wheaton for harmful algal bloom
A harmful algal bloom first detected almost two weeks ago at Herrick Lake Forest Preserve near Wheaton is apparently subsiding.
Water samples on Monday tested negative for the toxins produced by blue-green algae, district fisheries ecologist Dan Grigas said. But he cautioned that forecasts for relatively warm temperatures are ripe conditions for blooms to grow.
Toxic algae has been blamed for the deaths of dogs that swam in contaminated waters in Georgia and North Carolina, prompting state health officials to warn of the dangers for humans and pets.
"These are natural-occurring phenomena that happen typically in this time of year all over, so it's not just DuPage," Grigas said. "It can happen in a retention pond in a subdivision. It can happen in Great Lakes region on large-scale water bodies."
In DuPage, Herrick Lake first tested positive for microcystins, toxins released by certain freshwater blue-green algae, on Sept. 5. Tests confirmed a second, active bloom at Songbird Slough Forest Preserve near Itasca last week.
District officials warned on Facebook Monday that visitors should "continue to use caution, especially with children and dogs, as algae blooms are common this time of year."
"You can't tell by looking at the water if it has it, and tests aren't always reliable," a district Facebook post states. "Water may be clear one day and have the toxin the next."
Grigas recorded the most recent positive test at Herrick Lake last Friday. He plans on collecting water samples again Wednesday. Initially a small bloom developed into a lake-wide one at Herrick, Grigas said.
"These unicellular organisms are reproducing and forming colonies, and if the conditions continue to stay ripe, they'll continue to grow until they basically reach a carrying capacity and then crash," he said.
Blue-green algal blooms can look like spilled green or blue-green paint, according to the Illinois Environmental Protection Agency. While most blue-green algae are innocuous, some can produce the toxins that cause sickness in people and pets.
State health officials have advised the following: people should avoid contact with suspicious-looking water; don't let pets drink from the water; do not allow them to lick their fur or paws after swimming in water containing a blue-green algae bloom; and if you or your pet come into contact with a possible algae bloom, rinse off with clean, fresh water as soon as possible.
Symptoms of human exposure to algal toxins include rashes, hives, diarrhea, vomiting, coughing, or wheezing, according to the IEPA and the Department of Public Health.
Pet owners should seek immediate veterinary care if their dogs have been exposed to the toxins, according to a New York Sea Grant guide. Symptoms include repeated vomiting, diarrhea, loss of appetite, jaundice, bluish coloration of skin, dark urine or reduced/no urine output, stumbling, seizures, convulsions, paralysis, excessive drooling, disorientation, inactivity or depression, elevated heart rate, difficulty breathing, skin rashes or hives.
"There's not, as far as I'm aware, clear research on how long those toxins can persist in the water body," Grigas said last week. "But in talking with the Illinois EPA, they said up to and including a week is a safe time. So if the bloom stopped today, we would probably still be getting toxin levels in the water up to a week but obviously they would be diminishing returns."
DuPage ecologists have been able to test suspected blooms since 2015.
"It's been pretty common at a few of our lakes/ponds every year or every other year," Grigas said. "It doesn't seem to be increasing in frequency, duration or intensity compared to previous years."
The latest bloom in the forest preserve district persisted into October, Grigas said.
"We're getting toward the end of what I would call the blue-green algae season in September here," he said.