Natural shellfish habitats in local waters affected by human contamination have slowly been getting cleaner since 2003.

The Washington State Department of Health (DOH) cites more than 50,000 tests in 38 shellfish growing areas, showing a decrease in fecal pollution since 2003 as a good sign that Puget Sound waters are making a comeback — and along with them, shellfish.

“It’s encouraging to see improvements in Puget Sound’s shellfish growing areas,” said Secretary of Health Mary Selecky. “This is good news for shellfish lovers, our shellfish industry, and for those who have worked to reduce pollution.”

According to the DOH, state health workers collect water samples for fecal coliform bacteria at more than 1,200 sampling stations throughout the Puget Sound to verify that shellfish are safe to eat. The agency evaluated the areas they found to have been most affected by fecal pollution, with those areas being sampled at the same time and frequency for more than a decade.

Fecal coliforms are bacteria that live naturally in the intestines of warm-blooded animals, including humans. High concentrations of fecal bacteria in the water can mean that illness-bearing pathogens might be present. Shellfish ingest and store the bacteria as they filter their own foods from the water. People who eat the contaminated shellfish can become violently ill, and most often, when beaches and local waters are closed for shellfish harvesting, it’s because the fecal coliform level has risen too high.

The DOH credits the improvements in local waters to better management of sewage systems, agricultural waste, boating waste and stormwater runoff near shellfish areas. Many of the 38 areas highlighted by the DOH’s long-term studies have had scores of people working to improve the water quality. One large player in recent years has been the Puget Sound Partnership, which has made a goal of increasing the Puget Sound’s harvestable shellfish areas by 10,800 acres in the next ten years.