Jonathan Lake
Carver County, MinnesotaHypereutrophic
On the LakeGrade rubric Jonathan Lake fails the cutoffs — a TSI of 74 and persistent algal pressure put it in the bottom tier. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.
A TSI above 70 puts Jonathan Lake in hypereutrophic territory: visible blooms are common, and clarity rarely climbs even in early summer. The lake's maximum depth is not yet documented in state morphometric records — context for its physical structure remains limited. The lake's surface area is not consistently recorded across state datasets — physical context remains partial. Within Carver County's 40 graded lakes, Jonathan Lake ranks 26 — below the local median, though not at the bottom.
Jonathan Lake has no invasive species recorded in Minnesota state databases as of 2024, though prevention practices still apply at all access points. The fishery is panfish-dominated — bluegill, crappie, and sunfish among the 3 species documented for the lake. No formal public access is documented at Jonathan Lake — most use is by shoreline residents and their guests. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-10-23. Grade methodology: LakeGrade methodology.
Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
Very murky, less than 1.5 ft of visibility. Phosphorus level: 157.5 µg/L. Trophic State Index: 74.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.5 ft | F |
| Phosphorus | 157.5 µg/L | F |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 74 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Fish Species
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→ Best fishing times for Jonathan Lake (14-day solunar calendar)
→ Is it safe to eat fish from Jonathan Lake? (mercury & PFAS guide)
→ Jonathan Lake fishing regulations (limits, seasons, special rules)
Water Quality Trend: → Stable
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.016 m/yr | 5 |
| Phosphorus | ↓ Declining | +3.95 µg/L/yr | 5 |
Location
County Ranking
Ranked #26 of 40 lakes in Carver County
Nearby Lakes in Carver County
More Minnesota Lake Rankings
State Parks Near Jonathan Lake
Other Grade F Lakes in Minnesota
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Most recent sample: 2024-10-23
Monitoring stations: 1