Data collected by the Maryland Department of Natural Resources and Old Dominion University in September 2026 showed that the volume of hypoxia —waters with less than 2 mg/l of oxygen— was larger than average that month. Out of 42 sampling years, only two yielded higher hypoxic volume in September.
Observed hypoxia was confined to Maryland, but the timing of sampling notably impacted the results. Maryland waters were sampled before a passing Nor’easter. Virginia waters were sampled afterwards when waters were mixed and temperatures decreased.
September had 0.30 cubic miles of anoxia—waters with less than 0.2 mg/l of oxygen, which was slightly more than was observed in August, and three and a half times the September historical average.
I can't really think of anything unusual in late August and September that could have increased the hypoxia, but the answer is almost certainly weather related, by then, most of the nutrients to the bay had already been delivered.
But, if you squinch your eyes and look at curves in the graph above, they're not nice sinusoidal humps, but look like there are "side humps" on the spring and fall sides on all three of the long term lines.
Since this data was taken, we've had another near miss from a nor'easter, with extremely strong winds, and high tides. I assume that whatever remaining hypoxia has been mixed away.
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