Yes, we have water quality measurements for Lake Sawyer dating back to 1971. Between 1974 and 1993, however, we have a big data void. This was the period during which an experimental wastewater treatment plant with a "constructed wetlands" was put in place. The wetlands were designed to drain into Lake Sawyer via Rock Creek. It was a disaster. Water temperatures rose, lake water became cloudy and algae grew everywhere. Fish died, suffocated by the lack of oxygen. Fortunately, the treatment plant was eventually shutdown with city sewer then connected to King County metro sewer mains. Remarkably, after several years, the lake recovered and has been relatively healthy and stable now for the past 20 years.
Following is a bathymetric map of Lake Sawyer showing contour lines of equal depth much like a topographic map would show. Water quality samples are taken where we see the red X.

What can we learn in reviewing this history? I'm literally awash in data (no pun intended), so I will focus on several key measures over several posts, starting first with water temperatures. Colder is always better - less plant growth and higher levels of dissolved oxygen needed to support resident trout, kokanee, small mouth bass, large mouth bass and other pan fish.. Coho salmon that spawn in Ravensdale Creek and Steelhead that at least at one time spawned in Rock Creek also need colder temperatures as they pass through the lake on their way upstream. It's even more critical for juvenile salmon making their way downstream as they head for the ocean. Following is a chart I prepared tracking water temperatures measured 3 meters below the surface from 1971 - 1973 and then 1996 through this year. I included just summertime measurements for June and August.

To my surprise, despite higher ambient temperatures during recent summers, there is not a significant upward trend. If anything, the trend is down slightly.
Looking more closely at recent data, we find quite significant fluctuations throughout the year, but about the same levels as has been the case historically (graphs provided by King County)..


Weekly and bi-weekly data show somewhat higher spikes each year than do the longer term trend data. The best news - the data doesn't show a significant long term upward trend. Let's hope it stays that way. Next week, I'll focus on lake water clarity as measured by the Secchi instrument.