Some Perspective and Facts About Blue-green Algae on Delmarva

There are some stories in the news recently about blue-green algal poisonings of dogs.
By Robin Tyler

Some Perspective and Facts About Blue-green Algae on Delmarva: There are some stories in the news recently about blue-green algal poisonings of dogs. From 1990 to 2017 I was an aquatic ecologist with the State of Delaware, DNREC. I monitored and studied surface water quality (streams, ponds, lakes, rivers, bays) and the status of creatures living in the water and on or in the bottom, including blue-green algae blooms

Bluegreen algae blooms are not a new phenomenon and bluegreen algal poisonings long predate the internet and Facebook. The literature including scientific and general reading is vast and growing, highly technical, multi-faceted and overwhelming, even to someone with a fair amount of background on the subject. Getting one’s mind around this material and maintaining a feeling of informed concern rather than emotion and fear amidst very compelling stories, pictures and videos may be difficult. 

Red Mill Pond covered in blue-green algae .. Driscol Drones

In this article I’m going to cover some history of blue-green algae blooms as I learned it over my career and some of my experience working with them and perspective thus accrued. I’ll also make what I consider are some points useful to protecting one’s own safety and that of your animals from these blooms as they may be encountered on Delmarva. The greatest threat from the toxin produced by blue green algae is from ingestion – drinking the water. If you live where reservoirs or rivers are used for human drinking water then that is a related, but, different issue and worth learning about.


The writer: I’m a native of Princess Anne, MD on the lower Eastern Shore and grew up fishing in small freshwater ponds within bicycle distance in the 1960’s. I didn’t have a lot of freshwater fishing opportunities, but, the ones I did have were pretty good and a good way to keep a young teenager and his friends busy at something that the only harm they were apt to do would be to themselves. I don’t recall seeing anything in those ponds that looked like what I later came to recognize as bluegreen algae blooms. 

Red Mill Pond covered in blue-green algae .. Driscol Drones

Over time, I earned a bachelor’s degree in biology from Salisbury State College in 1981 and later, a master’s degree in environmental assessment from the University of South Carolina in 1987. My master’s thesis was an investigation of nutrient levels in coastal plain ponds in relation to aquatic plant abundance. Within a couple of years that degree and some work experience as a biologist at the South Carolina Department of Health and Environmental Control, Water Quality Monitoring Section led to what proved to be my career position with DNREC in what is now known as the Division of Water, Environmental Laboratory. By then, I had seen and began to learn about blue-green algae blooms, although I had yet to come across information implicating their toxicity. 

DNREC blue-green algae warning signs.


Some History: My first project as a new DNREC scientist in 1990 was a water monitoring study of several of Delaware’s public lakes/ponds under a USEPA, Clean Water Act (CWA), Clean Lakes Program (Section 314 CWA) grant. I discovered right away that some ponds/lakes developed bluegreen blooms every year and had been reported as doing so in the first surface water monitoring reports done in Delaware in the 1950’s. I started reading, going to scientific meetings and presentations and soon learned that the blooms could be toxic. In the early 90’s, I knew of only two University laboratories in North America that were doing testing for bluegreen algae toxin. There was also some literature on the subject from the United Kingdom. In the United States government environmental entities did not seem much, if at all engaged, at least not in the mid-Atlantic. Getting samples tested was impractical and to what end? There were no local reports of illnesses in either humans or animals linked to blue green algae and time went on with the blooms recurring each year and Delawareans continuing to swim without apparent ill effects in freshwater swimming holes that had been known to develop blue green blooms for decades. 


By the early 2000’s the testing technology had advanced to the point that more universities were starting to participate and some government laboratories soon followed. In Delaware this participation was largely driven by a new emphasis on “Harmful Algal Blooms” that was triggered by the Pfiesteria outbreak of the late 1990’s, which some may remember. A lot of federal monitoring and research funding was dedicated to Pfiesteria. It didn’t take long for the effort to spill over to other types of problematic algae, including the bluegreen algae. Also by then, more stories of illnesses in people and deaths of animals were coming in from around the country and region, more people were trained to look for the blooms and their effects, it was possible and practical to do some testing locally, the medical and veterinary communities were starting to become more aware and the internet had developed into the largest and most effective disseminator of information ever created.

Courseys Pond this summer … photo Robin Tyler


In light of the increasing information pertaining to toxic blue-green algae, many states and the EPA were getting on board with informing the public about this issue and in taking action to monitor and advise regarding the use of waters in which such blooms occur, or are likely to occur. Delaware DNREC issued some press releases informing the public about the issue. In 2009 DNREC formed a committee comprised of staff from DNREC, the Division of Public Health, the Department of Agriculture, City of Dover and City of Smyrna. The work of this group resulted in a topic page on the DNREC website, which is presently accessible by searching “Delaware blue-green algae” and signage posted at public ponds/lakes known to develop blue-green blooms. 

Ten more years have quickly passed and the people in that multi-entity committee have moved on. The stories we’re reading online draw out feelings we’d rather not have. It could have been my dog/s. Are my children in danger? Am I in danger? What is causing this? Why are we not being told about it? What are we not being told? Who’s to blame? How do we fix it? On and on…. Some may feel apathy. Some may decide to avoid using the water. What to do? What to say? 

Trap Pond blue green algae blooms thick like paint on the water’s surface .. photo Robin Tyler

Some Facts and Observations: On Delmarva bluegreen blooms typically begin to develop in sluggish to stagnant freshwaters in mid to late June, and persist into October. The most reliable visual characteristic is turbid, pea green colored water that may have a paint-like surface scum. Concentrations of toxin are generally highest in the scum, but, have been reported present in water without scum as well. 

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The greatest health threat is severe sickness to death in animals drinking out of bloom waters with the effects developing quickly, within an hour to a day of exposure. Humans swimming, water skiing or whatever activity that results in immersion may swallow a mouthful or two as well. That’s not good and they may get some gastrointestinal upset, but, they’re not lapping up the water like a dog and they’re not going home in the car licking it off their fur. They’re not getting the dose that a dog gets. In perspective, anyone who swam in Silver Lake in Dover until swimming was discontinued 10 years ago swam in bluegreen algae blooms as has anyone who water skied in Red Mill Pond over the past 40+ years.

Trap Pond blue green algae blooms thick like paint on the water’s surface .. photo Robin Tyler


There is information saying that bluegreen blooms can cause dermatitis from skin contact and respiratory problems from breathing aerosols coming off the water. I worked in contact with these blooms collecting water samples for many years and did not experience any such symptoms. Perhaps I was lucky. If you go to places that have bluegreen blooms and don’t develop symptoms be thankful. Also, beware that if you don’t feel well when in contact with a bloom or soon thereafter that feeling may have something to do with the bloom. Moreover, exposure of skin (particularly open cuts and wounds) to soupy warm water and bloom scums that are concentrated masses of organic matter is not without risk of infection from associated bacteria.


People may choose to fish in bluegreen blooms. Some of the ponds in Delaware that are known for big largemouth bass are also known for their annual blue-green algae bloom. Fish kills may occur during blue-green blooms. As I’ve investigated such kills and read investigations done by others, the kills are associated with extremely low dissolved oxygen. Warm water freshwater fish are quite tolerant of low oxygen levels and blooms seldom result in fish kills but they do happen. The low oxygen occurs because the massive quantity of living algae in the water consumes oxygen at night while bacteria consume oxygen 24/7 as they break down the dead algae that is also present. The result is that over a period of hours the amount of oxygen in the water may drop below the level necessary to sustain life. A day or more of continuous cloudy daytime condition is usually a contributing factor to these kills. 

Trap Pond blue green algae blooms thick like paint on the water’s surface .. photo Robin Tyler


One seldom mentioned characteristic of fish residing in blue-green ponds is their edibility. Some sources may say to avoid eating these fish. I don’t know of any information that is definitive that eating fish from a blue-green algae situation is actually harmful, but, I do know from my own experience that fish from blue-green waters have a very undesirable taste, and that such blue-green-related tainting of the taste of fish received a fair amount of attention in the scientific literature about 30 years ago. I found the taste of the first bite to be bad enough to spit it out and throw the rest away. So, if you must go and fish a blue-green pond/lake just throw em back. It’s not worth their lives or your work to clean and cook them. 


Do not be deceived by the presence of waterfowl swimming in bluegreen blooms without apparent ill effect. I have seen domestic mallards and geese swimming in waters that tested very high in toxin. I do not know why this is but it is. I would not take such an observation as a “green light” to let my dog swim with them.

Study up. Look at some state environmental websites. Many have a page dedicated to this issue. You may see some points I’ve touched on here. You will likely see additional points I’ve not brought up. A lot of work goes into developing these pages. They do a good job of presenting useful information in a measured, dispassionate way. Delaware and Maryland both have pages. Look at some of the websites from northern mid-western states (for example, Minnesota, Wisconsin, Nebraska). Their primary recreational areas are freshwater lakes and they have been dealing with this problem a long time. Bluegreen algae is bluegreen algae whether it’s Washington state or Delaware. 

Finally, learn to recognize bluegreen blooms when you see them. Don’t expect or depend on someone to warn you. There is no way that any program could have a sign anywhere and everywhere these blooms might pop up. Keep in mind that blue-green algae blooms have been occurring for much longer than any of us have been alive. Are the blooms more widespread? Are they more toxic than they used to be? These are difficult questions to answer definitively. What is true is that reporting of them is becoming more frequent and the damage they cause is better understood.
Following are some representative pictures of what to look out for. Understand that they are not all inclusive of the various looks that blue-green algae blooms may have. 


Robin Tyler

Trap Pond blue green algae blooms thick like paint on the water’s surface .. photo Robin Tyler
Trap Pond blue green algae blooms thick like paint on the water’s surface .. photo Robin Tyler
Trap Pond blue green algae blooms thick like paint on the water’s surface .. photo Robin Tyler
Courseys Pond this summer … photo Robin Tyler
Red Mill Pond covered in blue-green algae .. Driscol Drones
Red Mill Pond covered in blue-green algae .. Driscol Drones
DNREC blue-green algae warning signs.

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