For eleven days in August, the water off the east quay turned the color of pea soup, and Port Alden residents wanted to know why. Scientists at the East Bay Marine Lab say the answer is a wet July, a heat wave, and fertilizer that traveled a long way to get here.
The bloom was made up mostly of Microcystis, a cyanobacteria that thrives in warm, nutrient-heavy water and can produce toxins at high concentrations. Water chemist Anneke Visser, who led the lab's daily testing during the bloom, said toxin levels stayed below the threshold for a public health advisory throughout, though the lab recommended keeping pets out of the water. The lab tested samples twice a day at three points along the shoreline for the full eleven days, a pace Visser said the small staff could not have sustained much longer.
Where the nutrients came from
A wet July sent more runoff down the river than usual, carrying fertilizer washed off farmland roughly 40 miles upstream. Ten straight days above 90 degrees then warmed the harbor enough to let the algae multiply quickly once it arrived. Visser said the combination, rather than either factor alone, was what made this bloom larger and longer-lasting than anything the lab has recorded in a decade of monitoring.
"We've had small blooms before, gone in a day or two," Visser said. "Eleven days is new for this harbor, and that is what has us paying closer attention than the color alone would suggest.
The lab is installing sensors upstream this winter to catch nutrient spikes earlier, before a bloom is visible from the shore. Visser said the goal is a warning system that gives the city days, not hours, of notice, enough time to post advisories before a weekend when the waterfront is busiest.
Residents can reduce their own contribution by limiting fertilizer use on lawns near storm drains, Visser said, though she was careful to note that home lawns are a small factor next to agricultural runoff. "It's not the main cause. It still adds up across a whole city, and it's the one piece of this that residents can actually do something about themselves.
