WORCESTER — Indian Lake is off limits to the public because of something called cyanobacteria or blue-green algae.
But what is cyanobacteria and why is it dangerous for residents to swim, boat and fish in the popular Greendale body of water?
First off, cyanobacteria, also known as blue-green algae, are not actually algae. They are a photosynthetic organism that is naturally occurring, and when given the right environment can reproduce quickly, explained Jacquelyn Burmeister, a senior environmental analyst for the city of Worcester.
Indian Lake, with a high amount of nutrients — including nitrogen and phosphorus — and warm temperatures, provides the ideal environment for the cyanobacteria to bloom, she said.
While not all cyanobacteria are toxic, when there is an elevated presence of it, the presence of cyanotoxins becomes more likely. The ability to reproduce quickly is one of the problems cyanobacteria poses, said Burmeister.
“That’s a challenge for us because when they get too-high numbers, they tend to produce cyanotoxins,” she said. “Cyanotoxins have the ability to cause harm to humans. They include a variety of different toxins including neurotoxins, hepatotoxins, and dermatoxins.”
Cyanobacteria play an important role in photosynthesis, helping fuel marine food webs and a significant portion of the oxygen we breathe, explained Nathan Ahlgren, an assistant professor at Clark University and an aquatic microbial ecologist. However, some cyanobacteria make toxins that could be harmful to humans, pets and wildlife.
The most common type of symptoms include abdominal pain, vomiting and diarrhea if ingested, or irritation of the skin if it makes contact, said Ahlgren. However, symptoms and illnesses could become more severe if people or pets ingest or come in contact with these different toxins.
“Often toxins are made inside the cyanobacteria,” said Ahlgren. “There may not be a lot of toxins in the water but then eventually when they die they can release those toxins.”
The lake will remain closed until further notice after the city received test results showing elevated levels of cyanobacteria above recreational thresholds as determined by the Massachusetts Department of Public Health. People and pets should stay out of the water, and boat use and fishing have been discontinued until the water has been determined to be safe.
The city said in a press release that it will continue to test the water for both cyanobacteria and cyanotoxins.
Burmeister explained that in order for the water to be deemed safe and the beach reopened, the water needs to be tested for both cyanobacteria and cyanotoxins. Both need two consecutive tests showing low amounts in the water.
This is not the first time cyanobacteria have appeared in elevated levels in the lake, and instances of Indian Lake being closed due to the presence of cyanobacteria above the recreational threshold will be an ongoing management challenge, especially if temperatures increase and rain events become more intense, she said. One way to curb this is by reducing the presence of nutrients, especially phosphorus, in the water.
The city has developed systems to manage the levels, including using algaecide, but increased temperatures and nutrients from sources such as stormwater allow the cyanobacteria to bloom and reproduce quickly and in large quantities, said Burmeister.
These nutrients come from several places, including stormwater draining into the lake or goose feces washing off from the beach into the water, she said.
The city has taken steps to mitigate this, including installing fences that prevent geese — whose feces have high levels of phosphorus — from getting near the beaches, cleaning catch basins thoroughly and regularly, and rain gardens, which are gardens located near the lake that help filter stormwater and cool the water down before entering the lake, explained Burmeister.
The city is also building an alum dosing station on the mouth of Ararat Brook, which feeds Indian Lake, she said. The station would add alum, or aluminum sulfate, a coagulant used in drinking water treatment, to the river itself during rain events, which will deactivate phosphorus so it is not as available to the cyanobacteria. It will also help make the water more clear. Currently, alum is added directly to the lake but the station would allow the alum to be dosed more effectively directly to the source, she explained.
“Cyanobacteria are like plants. They do photosynthesis,” said Ahlgren. “They do better in warmer temperatures, and they do better if we give them nutrients. We have those two things combining, giving them favorable conditions to grow.”
Ahlgren also pointed to the use of fertilizers.
“A big source of those nutrients can be fertilizer from residential lawns and gardens,” said Ahlgren. “If we’re interested in trying to curb these blooms, our ability to cut back on our fertilizer use is going to be one of the more effective things we can do.”
It is difficult to give an exact number on when the issue will be resolved based on the blooms he’s seen in other places, but Ahlgren speculates it could be a matter of weeks.
He hopes that people will report the presence of algae or odd coloring in the water if they come across it.
“I always advise people, if you are going to a pond or lake, if the water looks really green or an odd color, don’t go in the water, don’t let your pet drink in the water,” said Ahlgren. “Mostly using common sense.”