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Map of Portsmouth Mine Pit Lake
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IntermediateShore entry

Portsmouth Mine Pit Lake

Minnesota, United StatesDirections
Open Water suggested3–137 m (10–450 ft) depthShore entry

Portsmouth Mine Pit Lake at a glance

Portsmouth Mine Pit Lake is an intermediate shore dive site in Minnesota, United States with depths of 3–137.2 m (10–450 ft). Typically most favorable Jan · from 3 years of archive data. Divers commonly see Northern pike, Rainbow trout, and Crayfish. Check the latest conditions and entry details before you go.

Favorable window now· until 19:00 · sunset 18:10

Wind forecast for this hour · 12:00 · run 12 h ago
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Tap a factor for its source and model point

Site hazards: Extreme depth beyond recreational limits, steep walls, cold water below thermocline, submerged trees and mine debris

Read the full hazards ↓

Dive windows this week

Lightest wind: Sun
Mon8:00–19:00 favorable

7 kn wind (7 kn wind)

Tue10:00–11:00 moderate, 12:00–14:00 moderate, 14:00–19:00 favorable

7 kn wind (7 kn wind)

Wed11:00–15:00 moderate, 15:00–19:00 favorable

9 kn wind (9 kn wind)

Thu8:00–11:00 moderate, 11:00–19:00 favorable

7 kn wind (7 kn wind)

Fri8:00–19:00 favorable

4 kn wind (4 kn wind)

Sat8:00–19:00 favorable

6 kn wind (6 kn wind)

Sun8:00–19:00 favorable

3 kn wind (3 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 7:18 · Sunrise 7:49 · Sunset 18:10 · some windows run past sunset

Source: Open-Meteo wind · updated 26 Oct, 00:26 GMT-5

Forecast only — always assess conditions on site.

Compare this weekend’s windows near Portsmouth Mine Pit Lake

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: Rainbow trout, Crayfish
Best time: May through October

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.

  1. January, 96% of days have historically been favorable, wind has typically been 9 knots, historically most favorable
  2. February, 89% of days have historically been favorable, wind has typically been 10 knots
  3. March, 85% of days have historically been favorable, wind has typically been 11 knots
  4. April, 73% of days have historically been favorable, wind has typically been 12 knots
  5. May, 83% of days have historically been favorable, wind has typically been 11 knots
  6. June, 82% of days have historically been favorable, wind has typically been 11 knots
  7. July, 90% of days have historically been favorable, wind has typically been 9 knots
  8. August, 87% of days have historically been favorable, wind has typically been 10 knots
  9. September, 94% of days have historically been favorable, wind has typically been 10 knots
  10. October, 77% of days have historically been favorable, wind has typically been 11 knots
  11. November, 88% of days have historically been favorable, wind has typically been 10 knots
  12. December, 86% of days have historically been favorable, wind has typically been 10 knots

January 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 seen at this site

Species noted at this site — 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.

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

A flooded iron-ore pit on the edge of Crosby in the Cuyuna Range, and at roughly 400-450 ft the deepest lake entirely within Minnesota. Its rock-filtered water gives up to 50 ft of visibility, and divers work the sheer walls, shelves and old mine features; most recreational dives stay in the 30-100 ft range while technical divers go far deeper. The Minnesota School of Diving in Brainerd leads group dives here several days a week from May through October.

shorewall

Extreme depth beyond recreational limits, steep walls, cold water below thermocline, submerged trees and mine debris

Reviews

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