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Oregon City presents findings on harmful algal blooms in Clackamas Cove
Summary
City water quality coordinator Marcos Kubo told the planning commission the cove’s summer isolation, sediment phosphorus release and invasive vegetation help drive cyanobacteria increases; staff recommended starting with invasive‑species removal and mechanical mixing before pursuing river‑exchange options.
Marcos Kubo, water quality coordinator for the City of Oregon City, told the planning commission the city has detected increased algal concentrations in Clackamas Cove and has preliminary evidence that internal phosphorus release from sediments drives summer cyanobacteria blooms.
Kubo said the cove becomes hydrologically isolated in summer — "it’s essentially cut off and acts like a lake" — when water depth drops below about 12 feet and the gravel bar at the entrance limits river influence. That isolation, combined with temperature stratification, creates low-oxygen conditions at the bottom that can release phosphorus from the top centimeters of sediment, he said. "We know the phosphorus is [the] limiting factor…
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