Tangier residents have gotten used to being cast as poster children for bad news on the climate front. Some scientists have predicted their Virginia Island in the middle of the Chesapeake Bay will succumb to sea-level rise before this century ends. But, thankfully, the watermen of Tangier have found a happier topic of conversation. Lately and without a ready explanation, the bay around them looked unusually clear.

At times, it’s been the clearest some folks like Mayor James “Ooker” Eskridge can remember in years. “It’s been the talk of the town some days,” the mayor said last week. “Lots of folks noticed it. … I was commenting to some of the other crabbers: We’ve got water like you’d see in the Caribbean.”

The mayor, a waterman himself, remembers first noticing the greater clarity toward the end of September. It’s typical for bay waters to sparkle more at that time as temperatures drop and algae growth slows. But this fall, even some old-timers have been struck by just far down into the water they could peer some days.

Now, scientists have become intrigued. Is it a one-time event or a sign of more to come? Chris Moore, senior scientist in Virginia for the Chesapeake Bay Foundation, is hoping it’s the latter. Clearer water is good for the bay’s health, Moore said. It allows more sunlight to reach the bottom of shallow areas. That helps restore underwater grasses, which provide food and habitat for crabs, fish and other creatures.

What’s not so clear is why Tangiermen and other folks who venture out on the Chesapeake began seeing the bottom for the first time – or at least the first time in a long while – in many places.

Moore’s theory for this is rooted in the weather. During long periods of dry weather in the late summer and fall across the mid-Atlantic, less water flowed into the bay from rivers, creeks and streams. Moore looked up a U.S. Geological Survey website that shows discharge rates in Harrisburg, Pa., for the Susquehanna River. During some stretches in September and October, the river was flowing at two-thirds the rate or less of its 125-year average. There were many more days of below-average than above-average readings.

The Susquehanna is the biggest contributor of all rivers to the bay’s fresh water, and it carries loads of nitrogen and phosphorus from fertilized farms and backyards. Those nutrients fuel the growth of algae, which in turn cause murkiness around places like Tangier. With less of the nutrients going in, Moore said, algae growth likely has slowed even more than normal.

Throw in the same lessened discharge from other waterways. Work in the fact that less runoff also means fewer particles of cloudiness-causing sediment entering the bay. Consider that more of the salty, clearer water of the ocean may be circulating up into the Chesapeake. And you start to get a picture of why Eskridge began noticing underwater stumps of trees that once anchored parts of Tangier before storms and tides chopped the island smaller.

Eskridge said he and other watermen knew the stumps were there in the murk, from memory: “Now, you could see them.” Bill Portlock, the Bay Foundation’s senior educator, had heard similar stories from his team of staffers who ferry students from grades 4 through 12 out on the Chesapeake. In far corners of the bay, from Baltimore harbor to the Rappahannock River in Virginia, they were reporting extraordinary clarity. He and his colleagues decided a helicopter ride was in order.