The total area of local waters where shellfish harvesting is prohibited or restricted increased by about 400 acres in the past year, according to figures for July 1, 2013 from the Virginia Department of Health.

A large part of this increase came from two bodies of water: 128.8 acres in North River, and 117.1 acres in Ware River.

In addition, approximately 98.9 acres were condemned in the Northwest Branch of Severn River and Vaughan’s Creek, where the total was zero acres in 2012; these water bodies have been on the list many times in past years, however. In 2011, for instance, 111 acres were condemned.

The state’s Division of Shellfish Sanitation takes monthly water samples to test for the presence of fecal coliform, and when levels pass a certain threshold, the taking of oysters and clams is not allowed. This is one measure of water pollution, and it has been in use in Virginia for many decades.

The division notes that oysters and clams are filter feeders and th...