Recognizing Algal Blooms or How to Recognize Algal Blooms

For Kansas waterbodies, we often categorize algae into two general groups: blue-green algae and all other types of freshwater algae. Algae are a normal part of a healthy aquatic community, and many species serve as food for other aquatic creatures. Blue-green algae are also a normal part of the ecosystem when they are present in low numbers. Both types of algae can bloom under the right conditions. Blue-green algae can sometimes create toxins that can cause a host of illnesses in humans and pets. This is discussed further in the Health Risks Associated with HABs.

Blue-green algae are often concentrated on or near the water surface. The following are some example images of blue-green algae blooms:

A harmful algal bloom with visible blue-green algae colonies in Central Park Lake.

A harmful algal bloom with visible blue-green algae colonies in Central Park Lake

A harmful algal bloom at Central Park Lake.

A harmful algal bloom at Central Park Lake

A severe harmful algal bloom at Webster Lake.

A severe harmful algal bloom at Webster Lake

You can view additional examples of blue-green algae (PDF). Keep in mind that many types of algae have some ability to float or sink within the water column, so a bloom may be more visible at one time of day and less visible at another. Wind and wave action, precipitation, and water current can also change their distribution within a waterbody. It can be difficult to tell the difference between blue-green algae and other types of algae. You can view examples of non-blue-green algae (PDF).

Blue Green Algae Examples

Blue Green Algae Examples (PDF)

Non-Blue Green Algae Examples

Non-Blue Green Algae Examples (PDF)

How to Confirm Blue-Green Algae

A trained biologist can examine samples with a microscope to determine the exact type and number of organisms present, and some laboratories are equipped to test whether toxins from blue-green algae are present. However, anyone can perform a stick test or a jar test to determine whether a given algae sample is likely to be blue-green or another type. You can use this instruction page to perform jar and stick tests (PDF).

How to Evaluate My Risk if I Want to Get in the Water

While there is no hard and fast rule, a general guideline is: "the worse it looks, the worse the risk is likely to be." The greener the water, the more likely it is that it is dominated by blue-green algae, and the risk increases for both humans and animals. Situations to avoid include strong green or dark green water, the presence of observable floating chunks (algal colonies), or the presence of surface scum. In addition, if there is an offensive odor or stench, then contact with the water body should be avoided. Under these conditions, the risk of exposure to harmful algae increases. If a lake has signage posted warning of the presence of a HAB, it means experts have made an examination of that lake, and KDHE is obligated to inform the public of the risks of water contact.

For More Information

This United States Geological Survey publication (PDF) offers a much more in-depth look into the different strains of blue-green algae. When in doubt, stay out.