Updated August 2026
Deepest Lake in Iowa: West Okoboji Lake (138.9 ft)
West Okoboji Lake is Iowa's deepest lake at 138.9 ft, per the Iowa DNR (Fish Iowa lake database + DNR bathymetric map). None of Iowa's lake pages carries a surveyed maximum depth yet, so there is no ranked table or map.
Browse all Iowa lakes for the water-quality data that does exist, or open West Okoboji Lake's report card.
No ranked-set map
A map here plots lakes with a surveyed maximum depth at their own coordinates. None of Iowa's lake pages carries one yet, so there is nothing to plot.
Sources and method
- Deepest lake: West Okoboji Lake, 138.9 ft, per the Iowa DNR (Fish Iowa lake database + DNR bathymetric map), 2026-07-30. West Okoboji Lake report card
Get updates on Iowa's deepest lakes
New grades and algae readings on these waters as samples come in. Unsubscribe anytime.
Frequently Asked Questions
What is the deepest lake in Iowa?
West Okoboji Lake, at 138.9 ft, in Dickinson County. Source: Iowa DNR (Fish Iowa lake database + DNR bathymetric map), 2026-07-30.
How are lake depths measured?
Maximum depth is the deepest point at full-pool water level, from state agency bathymetric surveys and, for reservoirs, dam-design records. The ranking uses surveyed depths only, never modeled estimates. Everyday water level can sit below the surveyed figure during drawdowns or drought. Mean depth, the average across the whole basin, is listed where a survey recorded it.
Why are some Iowa lakes so much deeper than others?
Lake depth depends on how the lake formed. Glacial lakes (common in MN, WI, MI, NY) were carved by ice sheets and can exceed 200 ft. Reservoir lakes (common in IA, MO, OK, KS) are shaped by river valley depth at the dam site — typically 50-150 ft at the dam, much shallower upstream. Flooded mine pits can be deeper still. Oxbow lakes and pothole lakes formed by river meandering or glacial pitting tend to be shallower, usually under 30 ft.
Does deeper mean cleaner?
Not directly, but deeper lakes tend to be cleaner on average. Depth creates thermal stratification in summer, isolating cold deep water from surface algal blooms. Deep lakes also resist nutrient resuspension from wind-driven sediment mixing. That said, many deep lakes still suffer from impairment if the watershed loads heavy phosphorus — each lake's page carries its grade and EPA impairment status.