Grand Lake is a highly nutrient-loaded hypereutrophic lake in Delaware County, Oklahoma. Water quality is graded F based on 2 sampling years through 2026. Compared to the 1 other monitored lakes in Delaware County, Grand Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Oklahoma DNR, last sampled 2026-06-23. Grade methodology: LakeGrade methodology.
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Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
Very murky, less than 1.6 ft of visibility. Phosphorus level: 760 µg/L. Chlorophyll-a: 384000 µg/L. Trophic State Index: 109.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.6 ft | F |
| Phosphorus | 760 µg/L | F |
| Chlorophyll-a (Algae) | 384000 µg/L | F |
| Trophic State Index (TSI) | 109 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
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Fishing Grand Lake
Location
County Ranking
Ranked #2 of 2 lakes in Delaware County
Nearby Lakes in Delaware County
Explore Grand Lake across LakeGrade
More Oklahoma Lake Rankings
Other Grade F Lakes in Oklahoma
More records, surveys & data sources
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Most recent sample: 2026-06-23
Monitoring stations: 16