Dissolved oxygen drops to critical fish-kill threshold

July 6, 2026Cross Timbers Transition

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The stream has crossed into hypoxia. Dissolved oxygen fell to 3.7 mg/L on a warm July afternoon — a level at which most fish cannot sustain activity, and below which die-offs become a real risk. At 26°C with low flow, the water holds little oxygen to begin with, and what remained was consumed overnight by algal respiration as darkness fell.

The margin for error has narrowed to nearly nothing. The north wastewater treatment plant is now in permit violation, adding oxygen-demanding effluent to a system already starved for it. This is not a theoretical worry — the conditions are here now, and they will repeat on every warm, low-flow day until late summer breaks.

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Dissolved oxygen plummets toward critical fish-kill threshold

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