NBM Dive Site Resource
Monrovia
Offshore Lake Huron, Michigan, United States
TECHNICAL DIVE ONLY — Monrovia is a Lake Huron shipwreck documented by NOAA at 140 ft / 43 m. This depth exceeds recreational limits and requires appropriate technical and decompression training.
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Aquatic life at this dive site
What divers may encounter
Three reviewed connections are featured here. Sightings vary by season, conditions, and chance, so they are never guaranteed.
Aquatic life research in progress
NBM is reviewing a likely local species for this position.
Aquatic life research in progress
NBM is reviewing a likely local species for this position.
Aquatic life research in progress
NBM is reviewing a likely local species for this position.
Site media
Photographs
Three views rotate from the published gallery on each visit.
Contributor media
Dive videos
Three featured video positions are reserved on every profile.Published reference location
Location map
The marker shows the public coordinates associated with this profile. Confirm current access, moorings, and departure details before the dive.Map data © OpenStreetMap contributors
Recent field observations
Diver-reported temperatures
Automatically checked observations from dives during the past 14 days. Three reports are visible at a time; scroll for more.A report that passes the automatic checks will appear here with the dive date, diver’s display name, and temperatures at each depth.
Reports are automatically checked for plausible dates, depths, and temperatures. They are observations, not forecasts; confirm conditions before diving.
Seasonal planning reference
Typical monthly conditions
Long-term averages, not a forecast. Actual air and water conditions can change quickly and may vary across the site.Moderate-confidence match — Matched by documented Great Lakes port/area. Air and surface-water values are regional planning averages. No bottom-water line is published because a comparable depth-specific record has not yet been verified.
| Month | Average air | Surface water | Bottom water | Bottom measurement depth |
|---|---|---|---|---|
| Jan | 20.0°F / -6.7°C | 35.5°F / 1.9°C | No reliable record | — |
| Feb | 20.7°F / -6.3°C | 39.5°F / 4.2°C | No reliable record | — |
| Mar | 29.3°F / -1.5°C | 40.5°F / 4.7°C | No reliable record | — |
| Apr | 41.2°F / 5.1°C | 36.4°F / 2.4°C | No reliable record | — |
| May | 53.4°F / 11.9°C | 38.4°F / 3.6°C | No reliable record | — |
| Jun | 63.2°F / 17.3°C | 44.9°F / 7.2°C | No reliable record | — |
| Jul | 68.2°F / 20.1°C | 59.6°F / 15.3°C | No reliable record | — |
| Aug | 66.6°F / 19.2°C | 65.9°F / 18.8°C | No reliable record | — |
| Sep | 59.0°F / 15.0°C | 61.9°F / 16.6°C | No reliable record | — |
| Oct | 47.4°F / 8.6°C | 54.1°F / 12.3°C | No reliable record | — |
| Nov | 36.6°F / 2.6°C | 46.9°F / 8.3°C | No reliable record | — |
| Dec | 26.6°F / -3.0°C | 42.6°F / 5.9°C | No reliable record | — |
NOAA NCEI 1991–2020 U.S. Climate Normals — Alpena, MI
1991–2020 climate normalsReview source ↗NOAA NCEI Coastal Water Temperature Guide — North Huron
Historical monthly station averagesReview source ↗Bottom temperature is never inferred from surface temperature. A blank month means no reliable depth-specific average is available. Data reviewed 2026-08-26.
Why divers know this place
Highlights
NOAA-documented Great Lakes wreck: Motor: ocean vessel; 448 feet.
Shipwreck-only module
The wreck
This section appears only on shipwreck records and brings the vessel, its loss, present condition, access, and responsible wreck-diving considerations into one place.
- Vessel type
- Motor: ocean vessel
- Vessel length
- 448 feet
History and significance
Despite improved charts, navigational aids, designated shipping lanes, radio telephones, and even radar, big ships still go down in the Great Lakes. Such was the case when the Liberian-registered ocean freighter Monrovia was rammed by the freighter Royalton during a heavy fog just outside of Thunder Bay. Monrovia went to the bottom in deep water. The wreck sits upright on the lake bottom and is largely intact except for the collision damage. Portholes are visible along the gangway in this image of the sunken vessel Monrovia . Rigging and superstructure of the ocean freighter Monrovia loom out of the blue depths of Lake Huron. Side scan sonar image of the ocean freighter Monrovia . A diver photographs the superstructure of the ocean freighter Monrovia . An view through a passageway inside the sunken freighter Monrovia .
Plan the trip
Dive boats that visit this wreck
Before you arrive
Access notes
Technical dive only. Confirm current conditions, mooring status, gas plan, decompression plan and operator requirements before departure. NOAA coordinates are reference points, not navigation instructions.
Plan within your training
Conditions and hazards
Depth beyond recreational limits, decompression obligations, cold water, limited light, changing visibility, entanglement and possible wreck overheads. Penetration requires separate wreck-penetration training and planning.
Independent resource notice
This record is a starting point for independent verification. Access, closures, moorings, weather, currents, depth, visibility, operator availability, and site conditions can change without notice. Confirm current information with the responsible operator, property owner, managing authority, or another qualified local source before planning or attempting a dive.