Grand Lake St Marys @ Intake
Mercer County, OhioView mapDirections
This is the name Ohio EPA records for this water. It can describe one sampling location rather than the water as a whole.
Ohio EPA publishes the water-quality measurements for Grand Lake St Marys @ Intake. Here is what has been measured.
- Hypereutrophic
- Public access
- Limited data
Grand Lake St Marys @ Intake in Mercer County, Ohio has water-quality measurements published by Ohio EPA, shown here as reported. Phosphorus: 395.5 µg/L. Chlorophyll-a (algae): 116.5 µg/L.
Grand Lake St Marys @ Intake is a highly nutrient-loaded hypereutrophic lake in Mercer County, Ohio. Limited fish-species data available. Public access is available with 4 public boat landings. Compared to the 1 other monitored lakes in Mercer County, Grand Lake St Marys @ Intake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Ohio EPA, last sampled 2022-09-21. Methodology: how these readings are compared.
What Grand Lake St Marys @ Intake is good for
From access and monitoring records, not editorial picks.
- Boat launch4 documented ramps
Swimming conditions
Readings onlyLimited data
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Grand Lake St Marys @ Intake is safe to swim in today is a call for the Ohio Environmental Protection Agency and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Grand Lake St Marys @ Intake
These are the measurements Ohio EPA publishes for Grand Lake St Marys @ Intake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Phosphorus 395.5 µg/L. Chlorophyll-a 116.5 µg/L. TSI 84.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 396µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 117µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 84 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Grand Lake St Marys @ Intake
Answers come straight from the public measurements and survey records on this page.
→ Grand Lake St Marys @ Intake water level: the live USGS gauge reading
Recreation & Access
- Grand Lake St. Marys State Park - Its It RampPublic
- Grand Lake St. Marys State Park - Mercelina ParkPublic
- Grand Lake St. Marys State Park - West Bank RampPublic
- Village of Montezuma Ramp FacilityPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Grand Lake St Marys @ Intake
Compare lakeside cabins, hotels, and vacation rentals near Grand Lake St Marys @ Intake in Mercer County, Ohio — 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. The water-quality readings cover nutrients and algae, not lodging. Cabins and rentals around Grand Lake St Marys @ Intake are listed below.
Top-rated places to stay near Grand Lake St Marys @ Intake
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Fishing Grand Lake St Marys @ Intake
Nearby Lakes in Mercer County
Frequently asked questions about Grand Lake St Marys @ Intake
Where is Grand Lake St Marys @ Intake?
- Grand Lake St Marys @ Intake is in Mercer County, Ohio. This is the name Ohio EPA records for this water. It can describe one sampling location rather than the water as a whole. Its water-quality measurements are published by Ohio EPA and shown on this page as reported.
What is the water quality of Grand Lake St Marys @ Intake?
- Grand Lake St Marys @ Intake in Mercer County, Ohio has water-quality measurements published by Ohio EPA, shown here as reported. Phosphorus: 395.5 µg/L. Chlorophyll-a (algae): 116.5 µg/L.
Is Grand Lake St Marys @ Intake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Are there boat ramps on Grand Lake St Marys @ Intake?
- Grand Lake St Marys @ Intake has 4 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Grand Lake St. Marys State Park - Its It Ramp, Grand Lake St. Marys State Park - Mercelina Park, Grand Lake St. Marys State Park - West Bank Ramp, Village of Montezuma Ramp Facility. Public access is listed as yes.
Can I fish at Grand Lake St Marys @ Intake?
- Grand Lake St Marys @ Intake has 4 documented boat landings in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Ohio's fish and wildlife agency, so check its current regulations before you go.
Explore Grand Lake St Marys @ Intake across LakeQuality
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Where this data comes from
30 measurements from 1 monitoring station, 2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Division of Surface water (Ohio)
21OHIO_WQX30 samples · 2022
Analytical methods
- Total Phosphorus After Block Digestion
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- 2130 B ~ Nephelometric Method
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Named boat-access points from the USGS National Boat Ramps inventory