Harmful Algae Blooms (HABs)

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- A harmful algae bloom, or HAB, occurs when a type of microscopic planktonic algae known as cyanobacteria, or blue-green algae, grows very quickly or blooms.

During a bloom, blue-green algae form films or coloration in the water.

Contrary to the name, blue-green algae blooms come in many colors but are most often some shade of green or brown.

Why be concerned with HABs?

Because some species of blue-green algae can, under the right conditions, produce toxins.

These toxins can affect the health of people and animals that drink water or even come in contact with the water.

In humans, symptoms of exposure to algae toxins include rashes, blisters, hives, eye and nose irritation, diarrhea, vomiting, abdominal pain, numbness of lips, tingling in fingers and toes, dizziness, and headache.

In animals, toxins can often cause staggering, difficulty breathing, convulsions, salivation, weakness, and vomiting.

In severe cases, animals can die from exposure to HAB toxins.

Harmful algae blooms occur most frequently during hot, dry weather in July, August, and September.

Ponds with lots of stagnant water, shallow depths, and high nutrient concentrations especially phosphorus from fertilizers, manure, or runoff are most likely to experience HABs.

Why do blue-green algae grow?

Like all aquatic plants, blue-green algae need only water, sunlight, nutrients, and transport to a pond to grow.

However, unlike many other aquatic plants, they've adapted to grow in both low and high light conditions.

Blue-green algae are exceptionally fast growing because they can move throughout the water to feed on nutrients, are able to process nutrients that other algae cannot, they're tolerant of many adverse conditions such as freezing and heat, they outcompete other types of algae, and they're rarely eaten by other aquatic life.

This photo shows one species of microscopic blue-green algae.

How can you identify a harmful algae bloom?

Blue-green algae blooms make the water look uninviting.

The pond's surface may look like spilled paint, pea soup, or floating scum with an oily sheen, or the floating scum may look like grass clippings.

The water may also be streaked with various colors, or there may be green globs floating just below the surface.

How can you distinguish blue-green algae from other types of algae?

Unlike filamentous algae, you can't pick up blue-green algae.

The films or growth typically dissipate or just leave a thin film on your hand if you try to touch them.

A harmless planktonic algae bloom is more likely to cause the water to become turbid or cloudy, as you can see in this photo, while typically HABs have floating scum layers that look streaky or paint-like, but the only way to properly identify blue-green algae is to look at a sample under a microscope.

There are many species of blue-green algae.

Some produce toxins, while others don't.

Can you see the three different shapes of the blue-green algae in this picture?

Each shape is a different species.

The algae that looks like grass clippings is called a Aphanizomenon.

The circular algae is called Microcystis.

The straight strand of algae is called Anabaena.

Although a microscope is needed for accurate identification of HAB algae species, there is a simple float test that you can use to identify many species.

Fill a clear bottle about half full with pond water from the surface of the pond.

Let it sit for about 30 minutes.

If a layer or scum appears on the water's surface as pictured, it's possible that a blue-green algae species is present.

Many pond owners think that their ponds are experiencing a harmful algae bloom when, in fact, other types of aquatic plants are growing.

One common plant often confused for blue-green algae is watermeal.

Watermeal is a very small floating plant that also blooms or grows quickly in mid to late summer and can often completely cover the pond.

To identify watermeal, pick up the floating specs on your hand.

They'll feel gritty to the touch.

Unlike this picture, it's best to use plastic gloves when picking up any floating pond scum just in case it's a harmful algae that may contain toxins.

How common are HABs in Pennsylvania?

Penn State Extension conducted research to learn more about the occurrence of harmful algae blooms in ponds across the state.

In 2015 and 2016, 100 water samples from 60 ponds were submitted for identification.

Researchers found that about 20% of the submitted samples contained at least one blue-green algae species, 73% had other algae or plants but no blue-green algae, and only 7% had no algae or plants present.

While this study clearly shows that blue-green algae capable of producing harmful algae blooms are present in some ponds, it's important to keep in mind that blue-green algae toxins will only occur when environmental conditions are just right for their rapid growth: hot and dry weather, stagnant, shallow water, and high nutrient concentrations.

So what should you do if you notice a harmful algae bloom in your pond?

Most importantly, make sure that humans and animals do not have any contact with the pond water until at least two weeks after the bloom disappears since the toxins can persist even after the bloom is gone.

Contact to avoid includes swimming in, drinking, or even touching the affected pond water.

Research has shown that it's best to not use herbicide treatments during algae blooms because the treatment may result in a greater release of algae toxins.

Once you have a HAB, simply restrict access to the water during the bloom, and then take steps to prevent algae blooms in the future.

Possible preventative steps include nutrient control, aeration, or use of aquatic herbicides when the algae growth is just starting and has not yet bloomed.