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The City of Portland, Oregon

Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Ave, Suite 613, Portland, OR 97204

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What's Outside Now: Mystery Blobs?


close up of a bryozoanLate summer and early fall is a time when some people out enjoying the water—like the cleaner Willamette River and Columbia Slough—might encounter these floating jelly-like blobs. 

They are called bryozoans and can be found washed up on shore, under docks or floating attached to sticks in the water.  Freshwater bryozoans can reach up to basketball size or larger this time of year! 

No, these are not scary blob monsters.  They are colonies of microscopic animals.  Each tiny animal is a filter feeder, which dines on a variety of plants and animals floating around in the river.  Bryozoans are harmless.  They do not sting or bite, but they are living creatures, so please don’t disturb them.

Bryozoan means “moss animal.”  They are named for their yellowish-green tint, which is created by algae on the colony.  Most bryozoans are marine, however in the Portland area, the species of Bryozoa are the freshwater Pectinatella magnifica.  They are not a sign of bad water quality—in fact, they do not live well in polluted water. 

bryozoan attached to stick in water  bryozoan with a hand for size reference







For more information about bryozoans, see:

And, learn more about the Columbia Slough, where you may be able to spot bryozoans this time of year.


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