From her dock overlooking James Island Creek, Mary Edna Fraser has painted this stretch of water at sunrise and sunset and every hour in between, capturing the subtle changes in lighting and ripples on the surface. A low-hanging live oak limb serves as her easel.

The scene looks different than when she and her husband moved here more than 30 years ago, just before Hurricane Hugo. Development drove away the egrets that once nested nearby. The water keeps rising. And the oyster bed on the opposite bank is rapidly shrinking.

But it’s what she can’t see that scares her.

The creek has become a toilet, almost always teeming with germs found in feces.

Researchers who’ve studied the problem say the few hundred septic tanks on James Island — some of them right along the creek — are likely a major culprit. And it’s not an isolated problem.