What is the water quality grade for Upper Pat Mayse Reservoir?

Upper Pat Mayse Reservoir in Lamar County, Texas received a water quality grade of C (Fair). Water clarity: 3.1 ft visibility. Phosphorus: 30 µg/L. Chlorophyll-a (algae): 20.4 µg/L.

Is Upper Pat Mayse Reservoir safe to swim in?

Swim with caution, moderate algae may be present. Upper Pat Mayse Reservoir has an overall water quality grade of C. Algae concentration (chlorophyll-a) is 20.4 µg/L. Always check local health department advisories before swimming.

Lamar County, Texas

Upper Pat Mayse Reservoir

Grade CFair · 3.1 ft clarity

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Eutrophic

Upper Pat Mayse Reservoir is a productive, nutrient-rich eutrophic lake in Lamar County, Texas. Water quality is graded C based on 2 sampling years through 2025. Compared to the 2 other monitored lakes in Lamar County, Upper Pat Mayse Reservoir ranks #1 for water quality.

Source: EPA Water Quality Portal sampling records, Texas DNR, last sampled 2025-09-10. Grade methodology: LakeGrade methodology.

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Swimming Safety

Swim with caution, moderate algae may be present

Water Quality Grade: C, Fair

Very murky, less than 3.1 ft of visibility. Phosphorus level: 30 µg/L. Chlorophyll-a: 20.4 µg/L. Trophic State Index: 58.

Metric	Value	Grade
Water Clarity (Secchi Depth)	3.1 ft	D
Phosphorus	30 µg/L	C
Chlorophyll-a (Algae)	20.4 µg/L	D
Trophic State Index (TSI)	58	Eutrophic

High nutrients, frequent algae, reduced clarity

Where to stay near Upper Pat Mayse Reservoir

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