Sewage treatment is important but it doesn't help when your infrastructure fails.
Read the below report and it will give pause.
https://www.centerharbornh.gov/sites...se_1152024.pdf
In addition the town of Wolfeboro added sewer capacity by adding to their existing spray irrigation fields what they called rapid infiltration basins near 19 mile brook. These basins very quickly failed causing nitrate levels to rise in the brook which leads to 19 mile bay.
Center Harbors sewage lagoons are also located above Lake Kanasatka.
It makes one wonder if there is leakage that is escaping notice. Blooms are being noticed in these specific areas.