The National Shellfish Initiative launched in 2011 has begun a number of initiatives that has helped restore the oyster populations across the US. Specifically in the Puget sound a large amount of research and development has been done to help the aquaculture industry in the area. $1 million has been contributed to help find and fix faulty septic systems, which are a large part of the non-point source pollution affecting the Puget sound. Research was also done to look at oyster sustainability to fight pollution and what was found that for each waterfront property, and the runoff pollution (provided they have a functioning septic system) a minimum of 200 oysters are needed to completely filter and maintain the cleanliness of the water.
http://www.nmfs.noaa.gov/aquaculture/policy/shellfish_initiative_homepage.html
http://www.psp.wa.gov/shellfish.php
Image: http://www.realscience.us/2012/08/28/oysters-help-filter-pollution-in-new-york-rivers/