I routinely look up historic photographs for work on the Washington State Department of Ecology shoreline website. The image below came up on the page when I opened it.
The site is the Port of Tacoma at Commencement Bay and captures an impressive phytoplankton bloom in July 2006.
Thea Foss Waterway at Tacoma
The last image below suggests a source - the sediment laden Puyallup River carrying sediment from Mount Rainier provides a nutrient source for the phytoplankton.