Crystal Lake
Marquette County, WisconsinOligotrophic
Crystal Lake earns an A — every scored parameter (clarity and phosphorus) rates among the best monitored waters in Marquette County. The two scored sub-grades — clarity and phosphorus — track close together, so neither one is dragging the average down.
A TSI value of 38 puts Crystal Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. At 60 ft of maximum depth, Crystal Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. At 119 acres, Crystal Lake fits the Wisconsin median for monitored lakes, with partial shoreline records. Among the 13 graded lakes in Marquette County, Crystal Lake ranks 2 — in the top quartile locally.
Eurasian watermilfoil is established at Crystal Lake, which can dampen recreational access and pressure the native plant community. Bass fishing is part of the appeal: the species list runs to 3, anchored by largemouth and/or smallmouth bass. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-10-30. Grade methodology: LakeGrade methodology.
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Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Crystal clear, you can see 16.8 ft down. Phosphorus level: 11.5 µg/L. Trophic State Index: 38.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 16.8 ft | A |
| Phosphorus | 11.5 µg/L | A |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 38 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 60 ft |
| Surface Area | 119 acres |
Fish Species
Click a species to see all Wisconsin and Minnesota lakes where it is found.
→ Best fishing times for Crystal Lake (14-day solunar calendar)
→ Is it safe to eat fish from Crystal Lake? (mercury & PFAS guide)
→ Crystal Lake fishing regulations (limits, seasons, special rules)
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Water Quality Trend: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.814 m/yr | 6 |
| Phosphorus | ↑ Improving | -0.26 µg/L/yr | 6 |
Location
County Ranking
Ranked #2 of 13 lakes in Marquette County
Nearby Lakes in Marquette County
More Wisconsin Lake Rankings
State Parks Near Crystal Lake
Other Grade A Lakes in Wisconsin
Washington County · Clarity: 11.8 ft
Washington County · Clarity: 12.6 ft
Walworth County · Clarity: 11 ft
Waukesha County · Clarity: 11.3 ft
Walworth County · Clarity: 20.2 ft
Kenosha County · Clarity: 10 ft
Oligotrophic Lakes in Wisconsin
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 2016. 1 station on file (most recent sample 2025).
Fish Species (DNR-rated)
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Most recent sample: 2025-10-30
Monitoring stations: 1