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Not all algae blooms are harmful and some look-alikes harmless

DuckweedThis is the time of year that algae grow in Michigan lakes. While some algae are indeed harmful, there are look-alikes that cause people to be concerned.

That was the case recently when West Michigan media got calls from people about suspicious looking vegetation near several Lake Michigan beaches described as a "sea of green."

EGLE staff jumped into action to test the vegetation. Turns out the green mass was duckweed - the smallest known flowering aquatic plant - and not algae at all, says Gary Kohlhepp, of EGLE's Water Resources Division.

Duckweed is common, native plant found in Michigan lakes and wetlands. After heavy rains, it can be transported downstream through rivers to other bodies of water.

While its appearance is alarming and its smell revolting when decaying, it is harmless to both people and pets.

EGLE has joined with the Michigan Department of Health and Human Services to produce a picture guide that includes harmful algal blooms as well as lake conditions commonly mistaken for harmful algal blooms (HABs). HABs can make humans and animals sick. Check out EGLE's HAB webpage for more details.

It is, however, impossible to know if algal blooms are harmful just by looking at them. To report suspicious-looking algae, call 1-800-662-9278 or email

Photo caption: Duckweed

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