Shallow Lake vs Third River Flowage Lake
Water quality, depth, fish species, and recreation comparison.
Shallow Lake has a higher water quality grade (A, Excellent) than Third River Flowage Lake (C, Fair). Both are in Itasca County, Minnesota.
Both Shallow Lake and Third River Flowage Lake sit in Minnesota. 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. The grades are meaningfully apart: Shallow Lake grades a A while Third River Flowage Lake grades a C. That two-letter spread reflects real underlying differences — different watershed inputs, different depth profiles, or different monitoring rigor.
For a recreational visitor, the wider grade gap is decisive — Shallow Lake 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?
Shallow Lake
Crystal clear, you can see 16.4 ft down.
Third River Flowage Lake
Moderate clarity, visible to about 6.9 ft.
Side-by-Side Metrics
| Metric | Shallow Lake | Third River Flowage Lake |
|---|---|---|
| Overall Grade | A (Excellent) | C (Fair) |
| Water Clarity | 16.4 ft | 6.9 ft |
| Phosphorus | 9 µg/L | 28.5 µg/L |
| Chlorophyll-a (Algae) | 3.2 µg/L | 5.5 µg/L |
| Maximum Depth | 85 ft | 69.8 ft |
| Surface Area | 539 acres | 56,471 acres |
| Public Access | Yes | Yes |
| Fish Species | 12 | 20 |
| Trophic State | oligotrophic | mesotrophic |
Bold value = better for that metric (lower phosphorus / chlorophyll = cleaner; higher Secchi / depth / species count = better).
Verdict
Shallow Lake wins on overall water quality with a Grade A versus Third River Flowage Lake's Grade C. Water clarity: 16.4 ft vs 6.9 ft. For more fish-species variety, Third River Flowage Lake edges ahead with 20 documented species.
Source: EPA National Aquatic Resource Surveys, 2026.