1
AFlathead Lake
Flathead County, Montana · 10.6 mi from Mary Ronan Lake East
- +Two grade letters higher (D → A)
- +Lower phosphorus (1.7 vs 15.8 µg/L)
Cleaner Lakes Than Mary Ronan Lake East
2 higher-graded lakes within 30 miles, ranked by grade improvement and proximity.
Mary Ronan Lake East carries a Grade D (Poor) water quality score. Within 30 miles, 2 lakes hold a higher grade. Flathead Lake (Flathead County, Grade A, 10.6 mi away) is the closest meaningful upgrade.
Reviewed by LakeQuality Editorial Team · Updated
2
BBig Arm Bay Lake
Lake County, Montana · 9.7 mi from Mary Ronan Lake East
- +Two grade letters higher (D → B)
- +Lower phosphorus (1.5 vs 15.8 µg/L)
Reading the cohort
Only 2 lakes within a 30-mile radius score better than Mary Ronan Lake East's Grade D. The narrow set of options reflects either a fairly clean lake to begin with or a region without a wide range of cleaner alternatives — the trip-planning decision is more constrained than the headline "cleaner lakes nearby" suggests.
Flathead Lake (Flathead County, Grade A) is the closest cleaner option at 10.6 miles from Mary Ronan Lake East — close enough to be a genuine substitute for most users, far enough that it isn't the same neighborhood lake. Worth the trip if water quality is the primary driver; less obvious if Mary Ronan Lake East is on the way to other plans.
The EPA water-quality grading combines clarity (Secchi depth), phosphorus, and chlorophyll-a measurements from state environmental sampling. A higher letter grade reflects measurably cleaner water on those indicators, not subjective beauty or access quality — a Grade A lake might have worse boat-launch facilities or shoreline access than a Grade C neighbor, so the ranking is one input alongside the rest of trip planning. See the methodology page for the full grading formula.
How this list is built
Every lake on LakeQuality has a calculated grade from EPA Water Quality Portal samples — secchi depth, total phosphorus, and chlorophyll-a measured against Metropolitan Council thresholds. To suggest cleaner alternatives, we filter lakes within 30 miles to those with a strictly higher numeric score, then rank by grade improvement with a small proximity tiebreak. Cross-state and limited-data lakes are excluded so the list stays locally relevant.