St. Mary’s City, MD – On Jan. 8 the tide dropped lower than usual, even for this time of year, in the upper St. Mary’s River. Lunar low tide was forecast for 10:14 am, when these photos were taken. But other events were more responsible for the extremely low tide.

The sun was within a couple days of its closest point to earth, causing additional gravitational pull. But the biggest impact comes from several days of northerly winds that has pushed the water out of the St. Mary’s River and out of the Chesapeake Bay. The result was a tidal reading in front of the St. Mary’s College of 2.3 feet below average low water. That’s -2.3′.

Coupled with the very cold temperatures overnight (some areas along the river recorded lows of 11 degrees), the impact on aquatic life, especially oysters, could be significant.

“Those animals with a means of transportation just move offshore to deeper waters,” said Bob Lewis, local advocate for oyster restoration. “Fish can swim away, but the oysters are stuck there, literally, and when the water level drops way down, those oysters become exposed to the frigid air. Many of them could freeze and die.”

The association’s three dimensional oyster reef has built a tolerance for low tide events into its design for up to one foot below average low water.

Thursday’s low tide exposed the top 12 to 16 inches of those higher reefs. Association staff surveyed several sites in the upper river and in some places natural oyster bars were left with areas sticking up out of the water. One of these natural bars is in front of the college’s River Center, and many of the oysters looked to be quite healthy and market size (over 3 inches), an encouraging sign.

Tidal events like this happen every winter. Coupling those events with extreme cold can spell death for oysters living near the surface.