MAHOPAC, N.Y. - This year, blue-green algal blooms have dashed many summer plans as Putnam County health officials have had to make repeated beach closures due to the toxic aquatic plant.

Even Lake Mahopac has not been immune. Its one public beach at the Mahopac Golf and Beach Club has been closed twice due to the presence of the nasty stuff.

Last week, officials from the county health department, along with members of Lake Mahopac Park District Advisory Board, held an informational meeting on blue-green algae at Mahopac Public Library to help educate the public.

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“I have been dealing with this since 2011 and when we closed the Golf Club beach originally, it was the first time I’d seen it on Lake Mahopac,” said Vince Perrin, a public health sanitarian with Putnam County Department of Health. “Lake Mahopac, in our eyes, is a little bit different—not because of the ecology or the size of it, but because it’s deep and cold. We have one regulated beach (Mahopac Golf) with a swimming area the size of this room and that’s our only eyes; it’s our only set of eyes on the beach. So, this year, we went out and had a few conservations with people on the private beaches. At Mahopac Woods, we saw a potential bloom floating in the middle of the water.”

The increasing number of harmful algal blooms (HABs) in Putnam and around New York State is not completely understood. Staff at the Department of Health have been busier than ever collecting and sending lake water samples for testing.

“We are working closely with town and beach personnel,” said Dr. Michael Nesheiwat, interim commissioner of health. “They are well-informed and able to quickly recognize these harmful algal blooms. When there is an overabundance of this cyanobacteria, the onsite personnel are able to shut down the beaches directly without a confirmatory visit by the health department.”

Perrin was accompanied at the meeting by fellow county health sanitarian Shawn Rogan, and both of them cautioned that while it is important to raise awareness of blue-green algae and take the necessary precautions, conditions on Lake Mahopac are not dire.

“It’s not the end of the world, the sky is not falling,” Perrin said. “But it does have an impact on our recreational use throughout Putnam County. Our main goal [of the meeting] is that you will have an appreciation for what it looks like, how you self-identify it, because the idea is you want to protect your family and your friends, and what to do when you see it.”

Toxic bacteria are naturally present in low numbers in lakes and streams. However, in warm, shallow, undisturbed surface water that gets a lot of sunlight, the bacteria can grow quickly and easily, creating a bloom. When this happens, floating scums on the water surface may appear, along with discolored water covering all or portions of a lake.

Health Department officials say they will continue to monitor the county’s 32 permitted bathing beaches this summer, while also responding to calls from town, village and summer camp personnel.

At last week’s informational meeting, a number of slides were shown to help people identify the substance, so they can report it.

“It’s called blue-green algae, but it doesn’t have to be blue and it doesn’t have to be green,” Perrin said. “Just because it’s ‘blue-green’ algae doesn’t mean those are the only colors you look for. It expresses itself differently depending on when you are and where you are and how early in the bloom you are. It goes by many different names. It is opportunistic in various conditions: stagnant water, warm water, lots of sunlight.”

Blue-green algae can range in color from green, blue, brown, yellow, grey, or even red.  So, contact should be avoided with any discolored water, with or without a floating covering or unpleasant odor. When the water clears, either naturally or by treatment, follow-up water testing must be conducted. Toxins can still be present even after the bloom looks like it has passed.

“Why are we scared of it? Blue-green algae release toxins and it can affect different people in different ways,” Perrin said. “Some people are more susceptible than others. And it’s not just toxins that are a concern. Some people are allergic to the proteins that are in the algae.”

Perrin said swimming in it and/or drinking it are two of the most obvious ways to be made sick by the algae, but they’re not the only ones.

“One thing that was noticed is that inhalation of the aerosolization of the water can cause short-term respiratory distress,” Perrin said. “If you are sitting next to the water and it is aerosolizing you are going to inhale it and it may cause short-term distress. It’s not like if you walk by the lake you are going to get sick.”

Perrin said sitting by on a beach while the water laps at the shore can aerosolize it, as well as driving a boat or watercraft through a bloom. He said 93 percent of exposure to the HAB is through recreation; the rest is occupational.

Some towns have opted to apply an algaecide, but they have the same precautions as any pesticide. Treatment methods, if any, are strictly a town decision, and application of an algaecide requires approval by the Department of Environmental Conservation (DEC).

What causes blue-green algae and why is it suddenly appearing on Lake Mahopac?

“Over the last 30 years, we’ve had a lot of runoff. We have improper storm-water practices,” Rogan said. “We want to make sure to treat our stormwater and get rid of the sediment, and more importantly, the phosphorous.  And failing septic systems are certainly a contributor because of all the nitrogen and phosphorous. Fertilizer on all these pristine lawns we have on Lake Mahopac [plays a role]. We use a lot of chemicals and a lot of herbicides.”

Rogan also said that the feces from waterfowl such as ducks and geese “doesn’t help” either. He cautioned against feeding the birds and attracting them to the lake. Someone in the audience noted that four Canada geese can equal one septic system.

Rogan said it was important that people learn to identify the algae and report it to the health department when they spot it. He said the DEC has plenty of photos of it on its website, so people learn what it looks like.

“It’s part of building the science; it builds a baseline data,” he said of why it should be reported. “We don’t want people calling if you see weeds, but if you see something different, something you’ve never seen before and it seems odd, [report it]. We want your eyes and ears… we can’t be out there.

“We have such little perspective about Lake Mahopac,” he added. “We just don’t see that much of the lake. It’s not about closing something down, it’s about education and public health protection—making sure we keep your children safe. Certainly, no one is saying close down all of Lake Mahopac. That’s not practical and it’s not likely. But [if it’s spotted] we can issue an advisory for certain areas.”

Rogan and Perrin said symptoms of blue-green algae exposure include temporary respiratory distress if it has been aerosolized and breathed in, rashes, but mostly gastrointestinal distress.

Sadly, Perrin said, it may be dogs that are at the most risk. They will swim in it and lick it off their fur, and even drink the contaminated water.

“There have been no human deaths [attributed to blue-green algae], but there have been dog deaths,” he said. “They are smaller with less body weight.”

Health officials said prevention efforts should focus on ways to control the level of nutrients the algae receive. These include reducing plant fertilizer use, promoting efficient septic systems operations and managing stormwater. These tactics are supported by the DEC, but much is still unknown about the causes of blue-green algae.

If you believe you’ve spotted a blue-green algal bloom on Lake Mahopac or any public lake in Putnam County, call the health department at 845-808-1390, visit the website at, or visit its Facebook page at and Twitter @PutnamHealthNY.