Gem Mary Lake
Gem Mary Lake in Orange County, Florida has a water quality grade of B (Good). Water clarity: 10.3 ft visibility. Phosphorus: 7 µg/L.
- Clarity
- 10.3 ft
- Typical in July
- 87°F
- Type
- Oligotrophic
- Trend
- ↑ Improving
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Gem Mary Lake is a cold, clear oligotrophic lake in Orange County, Florida. Water quality is graded B based on 1 sampling years through 2025. Overall water quality is improving over recent sampling years. Compared to the 319 other monitored lakes in Orange County, Gem Mary Lake ranks #197 for water quality.
Source: EPA Water Quality Portal sampling records, FDEP, last sampled 2025-03-18. Grade methodology: LakeQuality methodology.
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Swimming Safety
Grade onlyBacteria A
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Based on E. coli testing, Gem Mary Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 17 samples across 5 seasons.
This is a historical summary of past testing, not a current condition — bacteria levels change quickly, especially after rain. Always check Florida’s current beach and health-department advisories before swimming.
Water Quality Grade: B (Good)
Good clarity, visible to about 10.3 ft. Phosphorus level: 7 µg/L. Trophic State Index: 38.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 10.3 ft | Not graded |
| Phosphorus | 7 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 38 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Gem Mary Lake
Compare lakeside cabins, hotels, and vacation rentals near Gem Mary Lake in Orange County, Florida — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Gem Mary Lake
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Water Temperature
Gem Mary Lake typically sits around 87°F at the surface in July. Summer average is about 87°F. Usually warmest in Sep (about 88°F) and coldest in Dec (about 71°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 25 field readings (2010–2025) via the EPA Water Quality Portal. See the full Gem Mary Lake water temperature breakdown →
Fishing Gem Mary Lake
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.085 m/yr | 5 |
| Phosphorus | ↑ Improving | -0.4 µg/L/yr | 5 |
EPA Impairment Status
Gem Mary Lake is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit FL3168Z · Official waterbody report · Matched by proximity (1.83 km)
County Ranking
Ranked #197 of 320 lakes in Orange County
Nearby Lakes in Orange County
Frequently asked questions about Gem Mary Lake
Where is Gem Mary Lake?
- Gem Mary Lake is a lake in Orange County, Florida. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Gem Mary Lake?
- Gem Mary Lake in Orange County, Florida has a water quality grade of B (Good). Water clarity: 10.3 ft visibility. Phosphorus: 7 µg/L.
Is Gem Mary Lake safe to swim in?
- Based on E. coli testing, Gem Mary Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 17 samples across 5 seasons. That works out to a bacteria swim-safety grade of A — a historical summary of past testing, not a current reading. Gem Mary Lake has a water quality grade of B (Good). Bacteria levels can spike quickly after heavy rain, so always check Florida's current beach and health-department advisories before you swim.
What is the water temperature of Gem Mary Lake?
- Gem Mary Lake typically sits around 87°F at the surface in July, from 25 EPA Water Quality Portal field readings (2010–2025). That is a typical value for the month, not a live reading.
Explore Gem Mary Lake across LakeQuality
More Florida Lake Rankings
Other Grade B Lakes in Florida
Oligotrophic Lakes in Florida
Where this data comes from
52 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Submitting organization not recorded for these samples52 samples · 2020–2025
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database