Grand Lake St Marys @ Intake
Mercer County, OhioView mapDirections
Ohio EPA publishes the water-quality measurements for Grand Lake St Marys @ Intake. Here is what has been measured.
- Hypereutrophic
- Public access
- Limited data
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 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.
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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.
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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. Grade methodology: LakeQuality methodology.
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.
| Metric | Value | EPA condition class |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 395.5 µg/L | Poor |
| Chlorophyll-a (Algae) | 116.5 µg/L | Poor |
| Trophic State Index (TSI) | 84 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Current Conditions
USGS snapshot Sep 7, 2026, 3:15 PM from gauge 403204084342601 (Grand Lake St Marys near Celina OH). Station page ↗ — a live reading replaces this snapshot when the gauge responds. Missing live data is not an all-clear.
→ 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
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 a lake in Mercer County, Ohio. 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.
What is the water level at Grand Lake St Marys @ Intake?
- The USGS snapshot on this page for Grand Lake St Marys @ Intake is 870.8 ft of water-surface elevation, recorded Sep 7, 2026, 3:15 PM at gauge 403204084342601. Current Conditions hydrates a live NWIS reading from that same station when the gauge responds. A missed live fetch is not an all-clear.
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.
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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