Longitudinal data collection efforts can be very diverse indicators of change, and when they involve real-world observations and explanations of water conditions on the Sound from ferries, moorings and floatplanes you get a wonderful resource for educators, scientists and people who work on the water.
That's the Eyes Over Puget Sound report from Department of Ecology. Updated regularly, with great images and highlights, and with reports posted all the way back to 2011.
There's also data available, with methodology notes for the same period.