Love the links provided thus far, I'll just add that the Secchi transparency readings are quite similar between Winni and Sebago, so on paper they are quite similar if you take the Secchi tests to be a good indicator of water quality:
At present the water quality of Sebago Lake is good. However, the threats to the lake’s water quality
are increasing. While average total phosphorus is currently less than 6 ppb and Secchi transparency
varies between 8 and 12 meters, water quality data indicate that transparency has been declining
since 1990, and total phosphorus levels have been increasing since 2006.
LAKE WINNIPESAUKEE 2015 SAMPLING HIGHLIGHTS by UNH
Town Docks 7.9 meters
Church Point 9.4 meters
Grouse Point 9.6 meters
https://www.pwd.org/sites/default/fi...ion-report.pdf
https://extension.unh.edu/resources/...70_Rep9587.pdf