Green Lane Reservoir vs Lake Nockamixon

Both Green Lane Reservoir and Lake Nockamixon sit in Pennsylvania. A same-state comparison strips out the state-level water-quality regime as a variable: any grade differences here are about the lakes themselves, not the agencies grading them. Lake Nockamixon (C) is materially cleaner than Green Lane Reservoir (F). A gap that wide is unlikely to close in a single year of remediation work; it reflects multi-decade differences in the lakes themselves.

For a recreational visitor, the wider grade gap is decisive — Lake Nockamixon is the better water-quality choice. For a researcher, the gap is the interesting part: what is different about the two watersheds, and which of those differences is mutable?