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Map of Big Blue (Lester Milligan Park)
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Shore entry

Big Blue (Lester Milligan Park)

Iowa, United StatesDirections
Open Water suggested2–11 m (5–35 ft) depthShore entry

Big Blue (Lester Milligan Park) at a glance

Big Blue (Lester Milligan Park) is a shore dive site in Iowa, United States with depths of 1.5–10.7 m (5–35 ft). Typically most favorable Sep · from 3 years of archive data. Divers commonly see Bluegill, Crappie, and Largemouth bass. Check the latest conditions and entry details before you go.

Moderate window now· until 11:00, then favorable & moderate until 19:00 · sunset 18:13

Wind forecast for this hour · 8:00 · run 8 h ago
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Tap a factor for its source and model point

Site hazards: Silt, cold bottom temperatures (~60F at depth in summer)

Read the full hazards ↓

Dive windows this week

Lightest wind: Sun
Mon8:00–11:00 moderate, 11:00–12:00 favorable, 12:00–14:00 moderate, 14:00–18:00 favorable, 18:00–19:00 moderate

12 kn wind (12 kn wind)

Tue11:00–12:00 moderate, 12:00–13:00 favorable, 13:00–15:00 moderate, 15:00–19:00 favorable

11 kn wind (11 kn wind)

Wed8:00–9:00 favorable, 9:00–13:00 moderate, 13:00–17:00 favorable, 17:00–18:00 moderate, 18:00–19:00 favorable

11 kn wind (11 kn wind)

Thu8:00–19:00 favorable

7 kn wind (7 kn wind)

Fri8:00–19:00 favorable

8 kn wind (8 kn wind)

Sat8:00–15:00 moderate, 15:00–19:00 favorable

8 kn wind (8 kn wind)

Sun8:00–19:00 favorable

5 kn wind (5 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 7:11 · Sunrise 7:40 · Sunset 18:13 · some windows run past sunset

Source: Open-Meteo wind · updated 26 Oct, 00:22 GMT-5

Forecast only — always assess conditions on site.

Compare this weekend’s windows near Big Blue (Lester Milligan Park)

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, Largemouth bass
Best time: Summer (surface ~70F)

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, 77% of days have historically been favorable, wind has typically been 12 knots
  2. February, 67% of days have historically been favorable, wind has typically been 13 knots
  3. March, 49% of days have historically been favorable, wind has typically been 14 knots
  4. April, 38% of days have historically been favorable, wind has typically been 15 knots
  5. May, 70% of days have historically been favorable, wind has typically been 12 knots
  6. June, 68% of days have historically been favorable, wind has typically been 12 knots
  7. July, 87% of days have historically been favorable, wind has typically been 10 knots
  8. August, 80% of days have historically been favorable, wind has typically been 10 knots
  9. September, 91% of days have historically been favorable, wind has typically been 10 knots, historically most favorable
  10. October, 61% of days have historically been favorable, wind has typically been 13 knots
  11. November, 66% of days have historically been favorable, wind has typically been 12 knots
  12. December, 81% of days have historically been favorable, wind has typically been 12 knots

September 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 July 2026

Site details

Big Blue is a flooded clay pit of about 14 acres in Lester Milligan Park on the west side of Mason City, used heavily for open-water training. Attractions include a training platform at about 13 ft, several derelict vehicles along the east side, and a roughly 25 ft sailboat. Maximum depth is about 33-35 ft with visibility around 20 ft.

shorewreck

Silt, cold bottom temperatures (~60F at depth in summer)

Reviews

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