Levee breach in upper Mad River Slough floods lagoons, prompts shellfish sampling and precautionary closure
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Summary
District staff reported a levee breach near Seahorse Ranch that flooded lagoons, triggered a temporary precautionary closure of shellfish harvesting and prompted water sampling; agencies removed an aqua dam and district staff say lab results are still pending while they continue to advocate for growers.
District staff told the Humboldt Bay Harbor, Recreation and Conservation District at its regular meeting that a levee breach in the far upper channel of Mad River Slough, near Seahorse Ranch, allowed impounded water to flood lagoons and damaged shellfish nursery operations.
The report said the breach produced road flooding, washouts, increased turbidity and an observed fish kill. District staff said they dispatched consultant SHN to collect water samples and that some samples were routed through the California Department of Public Health to the local health laboratory. "We had a temporary precautionary closure in the bay for any of shellfish harvesting. It was released a little later the next day," staff said during the meeting. Staff added that not all test results are back and that agencies involved — including US Fish and Wildlife and their contractors — have taken actions that some growers find unsatisfactory.
Staff said an "aqua dam" had been placed as a temporary measure but that it failed when tides and currents changed; agencies later removed the device. District staff said their role is limited to advocacy and coordination and that they are allocating staff time and modest district resources to support sampling and communications with growers.
Commissioners asked technical questions about when flushing flows would reestablish normal conditions and what short- and mid-term fixes might be available. Staff emphasized that repair work must be accomplished by responsible agencies, some infrastructure (gated or screw gates) may still be closed and weather and ongoing high tides could prolong the problem. A public commenter asked that the District keep growers and neighbors informed and continue to pursue testing and stabilization.
The report was informational; staff did not ask the board for action at the meeting. Staff said they will continue to provide updates as lab results arrive and agency plans develop.