Lake Red Rock is Iowa’s largest inland lake, listed at 15,250 acres by the Iowa DNR. It is a reservoir; the largest natural lake is Big Spirit Lake, at 5,684 acres. The comparison below uses the DNR’s published surface areas and separates individual lakes from river pools and lake chains. It is part of our Iowa Lakes Database.
- The largest lakes in Iowa, by size
- Why other rankings give different acreages
- The largest reservoir vs. the largest natural lake
- Where the big lakes are
- Maps and access for a visit
- Frequently asked questions
- What is the largest lake in Iowa?
- What is the largest natural lake in Iowa?
- What are the three biggest lakes in Iowa?
- What are the Iowa Great Lakes?
- How big is Lake Okoboji?
- How many lakes does Iowa have?
The largest lakes in Iowa, by size
The figures come from the Iowa DNR Fish Iowa catalogue, checked on September 10, 2026. These are published reference areas, not measurements of today’s water level. Mississippi River navigation pools, combined lake-chain totals and surrounding park land are excluded.
| Lake | Acres | Type |
|---|---|---|
| Lake Red Rock | 15,250 | Reservoir |
| Rathbun Lake | 11,000 | Reservoir |
| Big Spirit Lake | 5,684 | Natural lake |
| Coralville Lake | 5,340 | Reservoir |
| Saylorville Lake | 4,970 | Reservoir |
| West Okoboji Lake | 3,847 | Natural lake |
| Clear Lake | 3,684 | Natural lake |
Other sizeable lakes include Storm Lake (3,097 acres in the DNR record, including Little Storm Lake), Lake Odessa (3,000), Tuttle Lake (2,268) and East Okoboji Lake (1,835). These use the catalogue’s lake-wide figures; Tuttle lies on the Minnesota border.
Why other rankings give different acreages
A reservoir changes size as its water level rises or falls. A flood-storage maximum is not interchangeable with a conservation-pool area, and different surveys can produce different reference figures.
For example, the USACE December 2019 water-control manual gives Saylorville 4,970 acres at elevation 836 feet using 2014 computations. The next page gives Red Rock 14,870 acres at elevation 742 feet using 2011 computations, while the DNR catalogue lists 15,250. USACE’s Coralville project description gives a 4,500-acre conservation pool; DNR lists 5,340. The table consistently reports the DNR entries rather than silently mixing these sources. They are not all measurements made in the same year or under identical conditions.
The largest reservoir vs. the largest natural lake
It’s worth separating the two. Lake Red Rock is the largest lake in Iowa, but it’s a man-made flood-control reservoir on the Des Moines River. The largest natural lake is Big Spirit Lake in the Iowa Great Lakes – a glacial lake renowned for walleye. Iowa’s deepest lakes, by contrast, are smaller: see West Okoboji (over 130 ft) and Brushy Creek (77 ft).
Where the big lakes are
Iowa’s biggest reservoirs – Red Rock, Rathbun, Saylorville, Coralville – were built by the Corps of Engineers for flood control on the Des Moines, Chariton and Iowa rivers, mostly in the central and southern parts of the state. The biggest natural lakes – Big Spirit, West and East Okoboji, Clear Lake, Storm Lake, Lost Island – are glacial lakes in the north and northwest, with the Iowa Great Lakes being the densest cluster.
Maps and access for a visit
Location is often more useful than an extra thousand acres when choosing a day trip. Saylorville is on the north side of Des Moines, Red Rock is near Pella and Knoxville, Rathbun is near Centerville, and Coralville is north of Iowa City. Big Spirit and the Okoboji lakes are in the northwest; Clear Lake is in north-central Iowa.
The official records below list boat access, beaches, trails and camping. Open a record for its location and facilities; most also include a downloadable lake map. Check the operator’s current notices before travelling, since a listed beach or boat ramp is not a promise that it is open today.
- Lake Red Rock — official DNR record
- Rathbun Lake — official DNR record
- Big Spirit Lake — official DNR record
- Coralville Lake — official DNR record
- Saylorville Lake — official DNR record
- West Okoboji Lake — official DNR record
- Clear Lake — official DNR record
Frequently asked questions
What is the largest lake in Iowa?
Lake Red Rock, a reservoir on the Des Moines River near Pella. The Iowa DNR lists 15,250 acres. Its area increases when the reservoir holds floodwater, so a flood-stage figure should not be compared directly with ordinary lake areas.
What is the largest natural lake in Iowa?
Big Spirit Lake, called Spirit Lake in the DNR catalogue, at 5,684 acres. It is one of the Iowa Great Lakes in northwestern Iowa.
What are the three biggest lakes in Iowa?
Using the DNR reference areas in this inland-lake comparison: Lake Red Rock (15,250 acres), Rathbun Lake (11,000) and Big Spirit Lake (5,684). Red Rock and Rathbun are reservoirs; Big Spirit is natural.
What are the Iowa Great Lakes?
A group of natural lakes around Spirit Lake and Okoboji in northwest Iowa, including Big Spirit, West Okoboji and East Okoboji. Their combined area describes a lake chain, not one lake, so the comparison above lists its larger members separately.
How big is Lake Okoboji?
West Okoboji Lake is 3,847 acres; East Okoboji Lake is 1,835 acres, according to their DNR records. “Okoboji” also names the surrounding destination, so check whether a quoted area refers to West, East or the wider Iowa Great Lakes.
How many lakes does Iowa have?
The answer depends on whether you count natural lakes, reservoirs, river pools and small ponds. The DNR lake search lists these different kinds of fishing waters; it is a more useful starting point for finding a lake than an unexplained statewide total.
Browse the full database by Largest Lakes and Small Lakes, see our best lakes roundup, or head back to the Iowa Lakes Database.
Article image: Sailing on West Okoboji Lake, Jeff Wilson, CC BY 2.0.
.jpg){kind=link}