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.
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Site hazards: Silt, cold bottom temperatures (~60F at depth in summer)
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Best: SunFavorable windowModerate window— no window
First light 6:19 · Sunrise 6:48 · Sunset 19:30
Source: Open-Meteo wind · graded 13h ago
Forecast only — always assess conditions on site.
Dated firsthand observations from divers — not current conditions.
No diver reports for this site yet. — one dated observation helps every diver after you.
Based on community reviews and site data. Conditions vary — always verify before diving.
What conditions have historically been typical at this site, month by month — not a forecast.
September hastypically 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.
Species noted at this site — not a promise of what you’ll encounter.
No dive shops mapped within 25 km. Know one? Add it to the map.
Data updated July 2026
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.
Silt, cold bottom temperatures (~60F at depth in summer)
Big Blue (Lester Milligan Park) ranges from 1.5 to 10.7 metres deep (5–35 feet) — a shallow dive. It is a freshwater site. Depths vary across the site, so plan your profile to your training and verify conditions locally.
Big Blue (Lester Milligan Park) 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.
The best time to dive Big Blue (Lester Milligan Park) is typically Summer (surface ~70F). Conditions vary, so check the latest reports and forecasts on the dive site page before your trip.
Divers at Big Blue (Lester Milligan Park) in United States commonly report sightings of Bluegill, Crappie, and Largemouth bass. Bluegill and Largemouth bass are recorded as common sightings, while Crappie 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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