Loading page content…
Loading page content…
Loading lake conditions…
Grand Lake St. Marys is a reservoir in Ohio. It covers roughly 13,500 surface acres (about 21 square miles). Fish documented in the area include Channel Catfish, Common Carp, Flathead Catfish, and Black Crappie. It reaches a maximum depth of roughly 16 feet at an elevation of about 870 feet. For this location, LakeRadar tracks an hourly and 7-day forecast, wind and gust outlook, water readings, fishing conditions, and activity scores for boating, paddling, and swimming. Other waters in the region include Ferguson Reservoir and Indian Lake. LakeRadar pulls readings from a mapped water gauge, so current water data is shown when the station reports. Forecasts for Grand Lake St. Marys come from the National Weather Service and refresh several times a day.
Updated
No active alerts for this lake as of the last check (Oct 9, 10:20 AM EDT). Alerts are re-checked automatically; see the official source for updates.
Overall Excellent (92/100) across 4 activities. Best right now: Boating (97/100).
How the score is calculated →Best excellent fishing window, averaging 95/100 across these hours. Wind 5 mph from the southeast. Dusk hours (19:00 local). Derived from the hourly forecast; official alerts are not forecast and are checked separately.
| Metric | 2p | 3p | 4p | 5p | 6p | 7p | 8p | 9p | 10p | 11p | 12a | 1a | 2a | 3a | 4a | 5a | 6a | 7a | 8a | 9a | 10a | 11a | 12p | 1p |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Temp (°F) | 59° | 63° | 67° | 70° | 73° | 74° | 74° | 76° | 74° | 72° | 69° | 65° | 64° | 63° | 63° | 62° | 62° | 61° | 60° | 60° | 59° | 59° | 59° | 61° |
| Wind (kts) | 4 | 4 | 4 | 4 | 4 | 3 | 3 | 3 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 9 | 9 | 9 | 9 | 8 | 8 | 8 | 8 | 9 |
| Direction | S | S | S | S | S | S | S | S | S | SE | SE | SE | SE | SE | SE | SE | SE | SE | SE | SE | SE | SE | SE | SE |
| Gusts (kts) | 7 | 8 | 8 | 8 | 7 | 7 | 7 | 7 | 7 | 8 | 9 | 11 | 13 | 15 | 15 | 16 | 16 | 16 | 16 | 15 | 15 | 15 | 15 | 16 |
| Precip % | 1% | 1% | 1% | 2% | 2% | 2% | 2% | 2% | 2% | 3% | 3% | 3% | 3% | 3% | 2% | 2% | 1% | 1% | 1% | 1% | 1% | 1% | 0% | 0% |
| Time | Temp | Wind | Gusts | Precip | Cloud | Condition |
|---|---|---|---|---|---|---|
| Fri, 10 AM EDT | 59°F | 5 mph S (180°) | 8 mph | 1% | 22% | Sunny |
| Fri, 11 AM EDT | 63°F | 5 mph S (180°) | 9 mph | 1% | 19% | Sunny |
| Fri, 12 PM EDT | 67°F | 5 mph S (180°) | 9 mph | 1% | 12% | Sunny |
| Fri, 1 PM EDT | 70°F | 5 mph S (180°) | 9 mph | 2% | 10% | Sunny |
| Fri, 2 PM EDT | 73°F | 5 mph S (180°) | 8 mph | 2% | 41% | Mostly Sunny |
| Fri, 3 PM EDT | 74°F | 3 mph S (180°) | 8 mph | 2% | 55% | Partly Sunny |
| Fri, 4 PM EDT | 74°F | 3 mph S (180°) | 8 mph | 2% | 43% | Mostly Sunny |
| Fri, 5 PM EDT | 76°F | 3 mph S (180°) | 8 mph | 2% | 33% | Mostly Sunny |
| Fri, 6 PM EDT | 74°F | 3 mph S (180°) | 8 mph | 2% | 29% | Partly Cloudy |
| Fri, 7 PM EDT | 72°F | 5 mph SE (135°) | 9 mph | 3% | 34% | Partly Cloudy |
| Fri, 8 PM EDT | 69°F | 6 mph SE (135°) | 10 mph | 3% | 45% | Partly Cloudy |
| Fri, 9 PM EDT | 65°F | 7 mph SE (135°) | 13 mph | 3% | 40% | Partly Cloudy |
| Fri, 10 PM EDT | 64°F | 8 mph SE (135°) | 15 mph | 3% | 54% | Mostly Cloudy |
| Fri, 11 PM EDT | 63°F | 9 mph SE (135°) | 17 mph | 3% | 47% | Partly Cloudy |
| Sat, 12 AM EDT | 63°F | 10 mph SE (135°) | 17 mph | 2% | 56% | Mostly Cloudy |
| Sat, 1 AM EDT | 62°F | 10 mph SE (135°) | 18 mph | 2% | 56% | Mostly Cloudy |
| Sat, 2 AM EDT | 62°F | 10 mph SE (135°) | 18 mph | 1% | 63% | Mostly Cloudy |
| Sat, 3 AM EDT | 61°F | 10 mph SE (135°) | 18 mph | 1% | 49% | Partly Cloudy |
| Sat, 4 AM EDT | 60°F | 10 mph SE (135°) | 18 mph | 1% | 60% | Mostly Cloudy |
| Sat, 5 AM EDT | 60°F | 9 mph SE (135°) | 17 mph | 1% | 63% | Mostly Cloudy |
| Sat, 6 AM EDT | 59°F | 9 mph SE (135°) | 17 mph | 1% | 52% | Partly Sunny |
| Sat, 7 AM EDT | 59°F | 9 mph SE (135°) | 17 mph | 1% | 64% | Partly Sunny |
| Sat, 8 AM EDT | 59°F | 9 mph SE (135°) | 17 mph | 0% | 66% | Partly Sunny |
| Sat, 9 AM EDT | 61°F | 10 mph SE (135°) | 18 mph | 0% | 66% | Partly Sunny |
| Sat, 10 AM EDT | 64°F | 10 mph SE (135°) | 18 mph | 0% | 77% | Mostly Cloudy |
Official National Weather Service hourly forecast. Showing 10 of 25 hours. Wind arrows point the way the wind is blowing; the compass point and degrees show where it comes from.
| Period | Today October 9, 2026 | Tonight October 9, 2026 | Saturday October 10, 2026 | Saturday Night October 10, 2026 | Sunday October 11, 2026 | Sunday Night October 11, 2026 | Columbus Day October 12, 2026 | Monday Night October 12, 2026 | Tuesday October 13, 2026 | Tuesday Night October 13, 2026 | Wednesday October 14, 2026 | Wednesday Night October 14, 2026 | Thursday October 15, 2026 | Thursday Night October 15, 2026 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Temp (°F) | 76° | 59° | 77° | 59° | 70° | 58° | 78° | 63° | 77° | 55° | 71° | 56° | 74° | 58° |
| Wind | S 5 mph | SE 3 to 10 mph | SE 9 to 13 mph | SE 12 to 16 mph | NE 5 to 14 mph | NW 6 mph | W 3 to 8 mph | SW 8 to 12 mph | W 13 mph | N 8 to 12 mph | E 8 mph | SE 7 to 10 mph | S 13 mph | SW 14 mph |
| Gusts | 9 mph | 18 mph | 24 mph | 28 mph | 25 mph | 12 mph | 14 mph | 20 mph | 20 mph | 18 mph | 15 mph | 18 mph | 21 mph | 21 mph |
| Precip % | 2% | 3% | 1% | 86% | 86% | 14% | 0% | 20% | 21% | 13% | 15% | 26% | 29% | 36% |
| Forecast |
Excellent for fishing (90/100), from 5 available inputs. Supporting this: Wind 5 mph from the south. 1% chance of precipitation. Not available from a verified source for this lake: pressure trend, water temperature. Confidence is moderate (74%) because some inputs are unavailable or older than ideal.
Excellent for boating (97/100), from 4 available inputs. Supporting this: Wind 5 mph from the south. Gusts to 8 mph. Not available from a verified source for this lake: visibility and conditions, verified water access. Confidence is moderate (84%) because some inputs are unavailable or older than ideal.
Good for sailing (85/100), from 4 available inputs. Supporting this: Gusts are within 3 mph of sustained wind, so the breeze is steady. No active official alerts for this lake. Not available from a verified source for this lake: visibility. Confidence is high (88%).
Excellent for kayaking (96/100), from 5 available inputs. Supporting this: Wind 5 mph from the south. Gusts to 8 mph. Confidence is high (90%).
Water temperature is not available from a verified source for this lake. No swimming score is shown without it.
Loading interactive map…
Individual boat ramp GPS coordinates are maintained under the jurisdiction of OH Parks & Wildlife Authority. Public boaters should verify seasonal launch water levels, gate hours, and daily vehicle/vessel fees before traveling.
Grand Lake St. Marys is an important freshwater reservoir in OH, known for its dependable sport fishery, open cruising lanes, and scenic shoreline. Recreational boaters and anglers share its waters alongside migrating waterfowl and native wildlife. Public facilities and natural resource management are overseen by state and local natural resource agencies.
Valid freshwater sport fishing license issued by Ohio Division of Wildlife (ODNR) is required for anglers age 16+. Digital license on mobile is accepted.
Current motorized watercraft registration mandatory. Practice Clean, Drain & Dry protocols: drain all livewells and inspect props before launching. Life jackets required for all passengers.
Public shoreline and boating access managed by State & Local Authorities. Verify seasonal gate hours, launch fees, and parking rules before travel.
High-speed motorboating, pontoon cruising, wakeboarding, and water skiing across main channels. Target gamefish include Channel Catfish, Common Carp, Flathead Catfish, Black Crappie. Morning hours typically provide optimal glassy conditions for kayak and stand-up paddleboard (SUP) touring.
Warm water temperatures, peak swimming, active watersports, and open full-service campgrounds. Highest weekly attendance; plan early arrivals on summer weekends.
Spring pre-spawn and fall feeding transitions create prime trophy angling conditions. Cooler air, lower boat traffic, and vibrant seasonal shoreline foliage.
Mild year-round outdoor climate. Uncrowded waters, active winter bass and crappie fishing, and open year-round boat launch access.
No external source rows are cited by the data currently shown on this page.
Updated
Scores are heuristics, not safety guarantees. LakeRadar scores summarize available conditions and are not a substitute for official warnings, local rules, or on-water judgment.
All telemetry for Grand Lake St. Marys is synchronized directly from authorized federal and state monitoring networks (USGS, NWS, NOAA, and state environmental authorities). Observations are strictly instrumented readings — unmonitored sensors are transparently disclosed rather than synthetic estimates.
Last source audit: Oct 9, 10:20 AM EDT