The water has warmed to 22.6°C this week, and dissolved oxygen has dropped to…

June 29, 2026Chesapeake Rolling Coastal Plain

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The water has warmed to 22.6°C this week, and dissolved oxygen has dropped to 7.1 mg/L—a sharp decline from 8 mg/L just four days earlier. Caddisfly larvae, which had shown signs of recovery in recent weeks, are now visibly stressed; these insects are highly sensitive to warm water and begin to struggle above 20°C. The pattern reflects a larger, decadal trend: the Potomac basin has warmed measurably over decades, and the summer window for clean-water insects keeps narrowing.

The pressure is not only thermal. The Washington Navy Yard upstream remains flagged for PAH violations this monitoring cycle, adding chemical stress to a system already strained by summer heat. Aquatic insects that survived the industrial legacy of the Potomac now face a narrowing margin between survival and collapse.

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