How Does an Oyster Filter Water?

July 18th, 2011 by Sarah and Krissy

An adult oyster can filter up to 5 liters or 1.3 gallons on water an hour. That’s equal to 60 two-liter soda bottles a day, for just one oyster!  Historically, oysters could filter the Chesapeake Bay’s entire water volume in less than a week.  Today, with 1% of the oyster population left in the Chesapeake Bay, it would take oysters nearly a year.

So how do oysters do it?

Oysters are filter feeders, meaning they eat by pumping large volumes of water through their body.  Water is pumped over the oyster’s gills through the beating of cilia.  Plankton, algae and other particles become trapped in the mucus of the gills.  From there these particles are transported to the oyster esophagus and stomach to be eaten and digested.

Once the oyster removes all nutrients, indigestible material is expelled as “pseudofeces” through the anus.  The pseudofeces are expelled from the oyster’s shell via a rapid closing of valves. The expelled particles swirl through the water and resemble a smoke ring.  These smoke rings are an indication that oysters are filtering the water and doing what they are meant to do.

How Can I Teach About Oysters?

Now that you know a little bit about oysters and how they filter water, share the knowledge with your students! Here are some resources and lesson plans to help you do so:

  • Particulate Matters: Filtering Mechanism Laboratory – This dissection exercise from the Maryland Sea Grant utilizes dye to allow students to see how an oyster is able to filter materials from the environment and selectively process them as food or pseudofeces.
  • Hunting for Hemocytes: Forms Function, and Microscope Techniques – This lesson from the Maryland Sea Grant can be paired with the Particulate Matters lesson to expand on student microscope techniques and learn more about oysters.
  • Amazing Oyster – Younger students can learn about oysters through this lesson that helps them build a 3-D oyster pop-out reef!
  • Oystering on the Chesapeake Explorations 1-5 and Explorations 6-10 – Oystering on the Chesapeake, from the Chesapeake Bay Maritime Museum, offers teachers’ multi-disciplinary lesson plans to introduce students in grades 4 through 6 to the economic, environmental, and cultural significance of the oystering industry. Whatever lessons within the curriculum unit you choose, your students are sure to enjoy this exploration about the region’s oyster industry and the challenges facing the industry today.
  • Oysters and a Clear Bay – In this lesson, students will learn about the oyster population decline and regulations, and will try to “out-filter” an oyster in a lab activity.
  • Time-lapse: Oysters Filtering Water – This 44 second time-lapse video shows oysters filtering a tank of water.

Please refer to Bay Backpack’s searchable teacher resources section for more oyster-related lesson plans

Sarah Brzezinski is the Chesapeake Bay Program's Fostering Stewardship and Education Workgroup Team Staffer. Krissy Hopkins is a former Chesapeake Bay Program Staffer and is currently pursuing her PhD in geology at the University of Pittsburgh.


  1. Sonia Gibson…

    I appreciate you sharing this article post.Much thanks again. Really Cool….

    Trackback by Sonia Gibson — November 24, 2011 @ 10:16 am

  2. Blanca Steib…

    I value the blog post.Really looking forward to read more. Really Great….

    Trackback by Blanca Steib — February 24, 2012 @ 3:07 am

  3. It’s very generous of you and I do appreciate this information.

    Comment by Azizbek — March 25, 2012 @ 7:29 am

  4. Thank you so much for this! :D Surprisingly, there aren’t too many things on the Internet about the actual anatomy of the oyster and how their filtering works. I must not be looking hard enough, haha.

    Comment by Guest — October 31, 2012 @ 11:18 am

  5. this is awesome it helped me with my classwork. thx

    Comment by michael smith — April 9, 2013 @ 8:01 am

  6. :D

    Comment by Frank trolinZ — October 23, 2013 @ 7:07 am

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