How deep is Mermet Springs?

Mermet Springs ranges from 4.6 to 36.6 metres deep (15–120 feet) — a deep dive at its limit. It is a freshwater site rated as advanced difficulty. Depths vary across the site, so plan your profile to your training and verify conditions locally.

Is Mermet Springs a shore dive or a boat dive?

Mermet Springs is a shore dive — you can enter from land. The entry is recorded as an easy walk-in. The entry area is recorded as sheltered from surge. Basic facilities are recorded at or near the site, and cell service is recorded as good. Entry details and parking notes, where known, are listed in the access section of this page.

Can beginners dive Mermet Springs?

Mermet Springs is rated as advanced difficulty, which may not suit new divers. Listed depths run from 4.6 to 36.6 metres (15–120 feet). Access is from shore, with the entry recorded as an easy walk-in. Consider your experience level, conditions, and local guidance before planning.

When is the best time to dive Mermet Springs?

The best time to dive Mermet Springs is typically Spring and fall for best visibility. Open most of the year, weather permitting; closed Wednesdays year-round, Tuesdays closed except by appointment in summer, and Sundays closed in winter (December-March). Busiest May-October. Conditions vary, so check the latest reports and forecasts on the dive site page before your trip.

What will I see at Mermet Springs?

Divers at Mermet Springs in United States commonly report sightings of Bluegill, Crappie, Grass carp, Blue catfish, and Largemouth bass. Bluegill, Crappie, Blue catfish, and Largemouth bass are recorded as common sightings, while Grass carp is reported only occasionally. Marine life varies by season and conditions—check the site page for recent diver observations and photos.

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AdvancedShore entry

Mermet Springs

Illinois, United StatesDirections

Open Water suggested5–37 m (15–120 ft) depthShore entry

Mermet Springs at a glance

Mermet Springs is an advanced shore dive site in Illinois, United States with depths of 4.6–36.6 m (15–120 ft). Typically most favorable Aug · from 3 years of archive data. Divers commonly see Bluegill, Crappie, and Grass carp. Check the latest conditions and entry details before you go.

Next window today· 8:00–19:00 · favorable · sunset 18:05

Wind forecast for this hour · 7:00 · run 7 h ago

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Tap a factor for its source and model point

Site hazards: Deep dark water below the thermocline, overhead environment inside the 727 fuselage (training required), entanglement on attractions, low visibility after heavy rains

Read the full hazards ↓

Dive windows this week

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3 kn wind (3 kn wind)

Mon

3 kn wind (3 kn wind)

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4 kn wind (4 kn wind)

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6 kn wind (6 kn wind)

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7 kn wind (7 kn wind)

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6 kn wind (6 kn wind)

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10 kn wind (10 kn wind)

Favorable windowModerate window— no window

Every forecast dive window each day, site-local time, from wind forecasts. Numbers under each bar are daylight averages.

First light 6:46 · Sunrise 7:13 · Sunset 18:05 · some windows run past sunset

Source: Open-Meteo wind · updated 25 Oct, 00:25 GMT-5

Forecast only — always assess conditions on site.

Compare this weekend’s windows near Mermet Springs

Recent diver reports

Dated firsthand observations from divers — not current conditions.

No diver reports for this site yet. — one dated observation helps every diver after you.

Dived here today — did the forecast match?

What Divers Say

Known for: Bluegill, Crappie, Blue catfish

Best time: Spring and fall for best visibility

Based on community reviews and site data. Conditions vary — always verify before diving.

Best months, historically

What conditions have historically been typical at this site, month by month — not a forecast.

January, 84% of days have historically been favorable, wind has typically been 9 knots
February, 84% of days have historically been favorable, wind has typically been 10 knots
March, 75% of days have historically been favorable, wind has typically been 11 knots
April, 72% of days have historically been favorable, wind has typically been 11 knots
May, 87% of days have historically been favorable, wind has typically been 9 knots
June, 98% of days have historically been favorable, wind has typically been 8 knots
July, 95% of days have historically been favorable, wind has typically been 7 knots
August, 100% of days have historically been favorable, wind has typically been 7 knots, historically most favorable
September, 97% of days have historically been favorable, wind has typically been 7 knots
October, 91% of days have historically been favorable, wind has typically been 8 knots
November, 87% of days have historically been favorable, wind has typically been 9 knots
December, 83% of days have historically been favorable, wind has typically been 10 knots

August has typically had the largest share of favorable days here. Conditions vary year to year — this is historical context, not a forecast.

Based on 3 years of archive data. Bar height shows the share of days each month whose conditions have historically scored favorably.

Marine life recorded at this site, by month

Recorded observations — evidence of past sightings, not a promise of what you’ll encounter.

Species seen here

Rough labels: “Commonly seen” usually means two or more recorded sightings near this site in public dive logs (GBIF), “Occasionally seen” one; “Seasonal” and “Rarely seen” come from dive-guide research. Not a measured rate.

Polyodon spathula recorded here Jun–Jul (3 records)
most recent 2012
Ictalurus punctatus recorded here Jun (2 records)
most recent 2012
Lepomis macrochirus recorded here Jun (1 record)
most recent 2012
Micropterus salmoides recorded here Jun (1 record)
most recent 2012

Newest record here: 2012. Counts are occurrence records near this site from public biodiversity datasets (GBIF), grouped by calendar month across all sampled years. Sightings vary — past records are context, not a prediction.

Fills & rentals nearby

No dive shops mapped within 25 km (16 mi). Know one? Add it to the map.

Data updated June 2026

Site details

Mermet Springs is a spring-fed former rock quarry of about 8.5 acres near Belknap in far southern Illinois, and one of the most famous inland dive sites in the country. Its signature attraction is the Boeing 727 used in the film 'U.S. Marshals,' resting with its tail at 15 feet and nose at 50 feet and open for trained divers to swim through, alongside many other sunken vehicles and training platforms. The quarry reaches about 120 feet deep and is run as a full-service commercial dive park.

shorewreck

Deep dark water below the thermocline, overhead environment inside the 727 fuselage (training required), entanglement on attractions, low visibility after heavy rains

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