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LakeSinkholeFreshwaterSource Checked

NBM Dive Site Resource

Middle Island Sinkhole

Alpena, Michigan, United States

NOAA-maintained mooring provides access to the Middle Island Sinkhole geological and ecological dive site in Lake Huron.

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Historic Picture Placeholder

Old-fashioned maritime line drawing reserved for a future historic photograph
Historic Picture PlaceholderHistoric photograph pending research and rights review
WaterFreshwater
AccessSeasonal mooring / boat dive
ExperienceAdvanced recreational
Maximum depthMooring anchor at 72 ft / 22 m
Best seasonMoorings generally installed about May 15 through October 1
VisibilityVisibility varies

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.

Profile connection reserved

Aquatic life research in progress

NBM is reviewing a likely local species for this position.

Profile connection reserved

Aquatic life research in progress

NBM is reviewing a likely local species for this position.

Profile connection reserved

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.
Illustrated scuba diver reserved for a future dive-site photograph
Dive Photograph PlaceholderDive-site photograph pending
Illustrated scuba diver reserved for a future dive-site photograph
Dive Photograph PlaceholderDive-site photograph pending
Illustrated scuba diver reserved for a future dive-site photograph
Dive Photograph PlaceholderDive-site photograph pending

Contributor media

Dive videos

Three featured video positions are reserved on every profile.
Dive-site video pending
Dive-site video pending
Dive-site video pending

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.
Published reference coordinates45.19873, -83.32795
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Map zoom level 1 of 11

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.
Automatically checked
No recent diver reports from the past 14 days

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.

Diver field observation

Report temperatures

Reports publish automatically when the date, depths, and temperatures pass the checks. You must be signed in to submit.

Depth readings

Why divers know this place

Highlights

Freshwater sinkhole geology and unusual microbial ecology.

Regional context

Located within

Dive AreaThunder Bay National Marine SanctuaryAlpena, Michigan

Inventory source: Thunder Bay National Marine Sanctuary Mooring Buoys

Open area profile →

Before you arrive

Access notes

Check NOAA’s live buoy status before departure; mooring coordinates are 45°11.924 N, 83°19.677 W.

Plan within your training

Conditions and hazards

Cold water, changing visibility, weather, boat traffic and sensitive benthic habitat.

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.